That is a bad example. Explaining how something functions doesn't explain what it is for. Tires are for the purpose of rubber. Tires are for cars and they are made of rubber.

Electricity is in a socket but that is not why it is there.

Your brain doesn't exist for you to tie your shoes.

Engines are not cars

So, feelings are for not the purpose of chemicals to exist.

I think asking things like "what it is for" makes too big an assumption (it assumes that there is some kind of purpose external to the thing being described). Why can't the brain be a self-contained unit? Why can't our feelings be synonymous with chemical and electrical interactions? Oh sure we'd like to think our thoughts and feelings are more than just physical stuff, but IMO that's just human ego (it reminds me of this one philosophy class, when a student said she believed in evolution -- except for human beings). As Daniel Dennett said, the continuity of nature is not going to permit one species to have miracle stuff in their brain. Does the idea that we are ultimately mechanical make you feel less valued?

It is too big of an assumption. Each assumption made is only a piece of information. Reality always makes things more complicated. A car is made with an engine. A cars general purpose is transportation. A car can also represent ego. A car can represent technology. a car can represent modernity. Defining a car’s engine doesn't devalue any of those things. Describing the human meat bag as a meat bag does devalue us. We, unlike the car, have conscience. We, unlike the car, feel. Ego is a big part of it. Not getting into the 'importance' of humans over other living things here. Just that life is described by mechanics but that doesn't mean it is just mechanical. Even fire has a purpose.

Sea squirts feed by taking in water through the oral siphon. The water enters the mouth and pharynx, flows through mucus-covered gill slits (also called pharyngeal stigmata) into a water chamber called the atrium, then exits through the atrial siphon.
http://en.wikipedia.org/wiki/Ascidiacea

Purpose implies an aim or an intention, so to hold the idea that humans to have 'a purpose', other than the obvious natural one, implies that there is some goal that humans were 'designed' to fulfill.

It is too big of an assumption. Each assumption made is only a piece of information. Reality always makes things more complicated. A car is made with an engine. A cars general purpose is transportation. A car can also represent ego. A car can represent technology. a car can represent modernity. Defining a car’s engine doesn't devalue any of those things. Describing the human meat bag as a meat bag does devalue us. We, unlike the car, have conscience. We, unlike the car, feel. Ego is a big part of it. Not getting into the 'importance' of humans over other living things here. Just that life is described by mechanics but that doesn't mean it is just mechanical. Even fire has a purpose.

Purpose implies an aim or an intention, so to hold the idea that humans to have 'a purpose', other than the obvious natural one, implies that there is some goal that humans were 'designed' to fulfill.

We don't sit on the see floor and suck in what we can. We don't hide in the grass and wait for a sick animal to pass by. We actively engage and modify the world around us and are actively moving in the direction of expanding that outside of our world. That is purpose. It may not be 'the purpose' but you can't say that we are an ant leaving the nest and returning with food for the colony.

What do you mean there is no argument in that regard? So, I have to look outside and pretend it doesn't exist? I have to look outside and see all of the manmade recreation of the environment to suit our purposes and pretend it means nothing but ... but what? Human behavior is not as random as it appears right. It is predictable. We have rational predictions of what has happened and will happen with societies. That can't happen in total randomness. The basic assumption of natural selection and the argument against unguided evolution is the order from chaos and all of society follows that same line. Natural selection and the complexity of the human brain does not need an intelligent creator to get there right. Society is moving and has always been moving in the direction of controlling the entire planet and most likely pulling into a single world government. It has been self-organizing for centuries. That is more of a sense of purpose then you are willing to grant it. Where is the drive at? I personally don't like the one world government path as I don't trust the people who will be in charge. So, the need of an opposition exists. There are a lot of people that feel that way. The end result will be a more powerful single government that is able to overcome its opposition.

How do you not see purpose in this? I didn't mention religion or theology or anything spiritual. Without any of that do you still not see purpose?

I don't think purpose is what you're talking about here; instead you seem to be talking about ability. All living organisms have a purpose (which is almost universally to exist and reproduce). Humans are nothing special in this regard. The only thing different is that we are more capable of modifying our environment. Of course this could all change - the next meteor strike could wipe out humanity in a stroke.

The only thing different is that we are more capable of modifying our environment

Purpose denotes an intent....and thereby an intelligence in directing the creation of such an advantage.

Compare with an effect.

Is the purpose of a tree falling across a river to give animals a dry crossing.. or is that the effect?

Is the purpose of having long arms to scratch one's ankles without bending over, or is that the effect? Of course long arms also has the effect of reaching a few more pieces of tasty and nutritious fruit than a short armed runt.

And I can still scratch my ankles.

Different!
The conclusion you reach that it is irrelevant is without justification. You are placing a value judgment of 'not valuable' on the different ability to modify the world as we see fit which has been working over thousands of years toward the unification of a worldwide dominance and a definite eye on the universe.

Your conclusion that it is 'only because we can' equals 'non valuable' in the hierarchy of intentions and purpose does not make sense. We “can” therefore we are without purpose?

Or are you trying to say that our natural organization of society and consistent domination of our environment is meaningless and if we would have been sea slugs with legs the same thing would have happened? There is no evidence to support a lack of purpose.

I'm saying that our purposes are essentially no different from the sea squirt: it is to survive and reproduce

That is absolutely not true. Show me the law of the sea squirt. Your words again... "since we know..." We... and Know... differences again.

The only reason for the 'man is no more unique in the universe than the sea squint' is because of an attempt to create a morality from the natural world. If we are no more 'special' than a dust mite and we only exist to breed there is nothing sacred, unique, or special about humans. So, if we need to cull the heard. It's for the best. It is an attempt to remove the survival part of humans. Just bugs to be exterminated when usefulness is outlived.

Our species, our culture, our way of living and surviving is important to us, but only to us.

Or are you trying to say that our natural organization of society and consistent domination of our environment is meaningless and if we would have been sea slugs with legs the same thing would have happened?

There is no evidence to support a lack of purpose.

There is no evidence to support a lack of purpose.

You have it backwards. Part of the difficulty in proving a negative is that there nothing to refute.
It's for those making the claim to provide sufficient warrant to support it.

There is no evidence to support a lack of purpose.

And again, going outside and looking at the streets, cities, governments, technology, and pretty much everything humans have created isn't enough evidence for you. Doesn't need explaining. The sea slugs just didn't have legs.

And therein is the difference in world views... the concepts that one argues from rather than about.

The religious person takes it as a matter of faith and sees intelligent reason behind most things. Enthalpy.

The a-religious takes it as a matter of faith that events unfold largely by accident. Entropy.

Perhaps the secular humanist bridges the two by taking the random accident of humans emerging and forming societies that are capable of then creating a purpose for themselves and ordering the cosmos accordingly.