Reading Kant's Groundwork of the Metaphysic of Morals is giving me this experience almost every night I read it. I'll probably regret saying this but last night I was so moved by what I read I was almost in tears! Crazy isn't it? How can philosophy have that much of an emotional impact? I don't know. I have no explanation...therefore god. Now I go through the day waiting for the moment that I get to read more Kant. There must be something wrong with me! Anyway, lets talk about Kant, shall we?
So far so good. Next Kant tells us that people are also ends in themselves; that is, they have value in themselves and there is value in their own aspirations (i.e., ends). Because people are ends in themselves we can never use them as means to an end to which they don't consent. This is a common argument against slavery, for instance; people are being forcibly prevented from pursuing their own ends and are being used as a means to someone else's end.
In our modern ethical framework this idea is fairly standard (thanks to Kant). But Kant takes his argument one step further and says that if we are going to have a supreme practical principle of morality then it must be one that is directed at an end (i.e., something with intrinsic value) common to every person. What could possibly meet this requirement? For Kant, the only end with intrinsic value that can be held in common for all is that of humanity. From this idea he derives another formulation of the Universal Law: Act in such a way that you always treat humanity, whether in your own person or in the person of any other, never simply as a means, but always at the same time as an end.
I think it's important that he includes humanity as an end it itself as a consideration in our actions rather than simply treating individuals as ends in themselves. This is what I really love about the formulation. Consider what morality would look like if we didn't have the stipulation about treating humanity as a common end in itself: in this case all moral laws are negative; that is, they are restrictions on interfering with the lives others (without consent). For instance, most of the laws will take the form, of "do not restrict people from accumulating wealth; do not force people into labour; do not steal others' property, do not harm others, and so on.
Now consider the implications of having the additional consideration of harmonizing with humanity as an end in itself--not simply avoiding conflict with it. Now we can include social obligations. For instance because charity is in harmony with humanity as an end in itself it now becomes a moral duty. We can even argue that (and many have) most of what are now considered basic human rights arises from this notion of harmony with humanity as an end in itself (i.e., humanity has intrinsic value).
Libertarians like to argue that charity should be voluntary and thus should not be a moral duty and especially not a legal duty (via taxation). I'm sympathetic to Kant, that we do have moral duty to help those in need, especially when we are in a position to; this duty is in harmony with advancing humanity as an ultimate end. But I guess you could argue that your personal desires and rights are more important than those of all of humanity...Ah! The compassion! I think it would be a very interesting study to see how much the average self-identified Libertarian actually gives to charity (both as a percentage of income and actual value) compared to other self-identified groups. If someone knows of such a study, let me know.
In defense of the Libertarians I suppose at the end of the day it is a naked assertion that humanity has intrinsic value but it's a pretty harsh moral landscape if we don't adopt this position. Also--logic alert! this is not an argument!--suppose we assert the opposite is true: try saying out loud, "humanity has no value"...go ahead! do it! I'll wait. Doesn't that just strike you as wrong? Not that emotional responses mean anything but when I say it, it doesn't sit well with me; it makes me feel like I would if I farted really loud really during a a moment of silence at a funeral service.
As an aside, in experimental ethical philosophy this phenomena is known as the "Yuck" factor. It applies to situations where we can't point to what it is about an act that makes it wrong yet it incites some sort of feeling of moral revulsion in us. And if I were a theist I'd end with...and therefore, god exists.