I am a life-long Agnostic. Athiesm is to me as untenable as any religion, due to the ignorance of man. But as for the root question of how one can have socially conservative views as the result of personally constructed morality versus that installed by religion, I think there isn't much difference between Agnosticism and Athiesm.
Personally, I consider myself to have certain strongly conservative social views, as well as some strongly liberal ones. However, being agnostic I think adds a layer to how these views translate to political positions. That is, agnosticism is centered on the acceptance of ignorance as being greater than knowledge...i.e., as mortal humans, what we can ever know will be an infinitely small portion of all knowledge that is, and thus, we must accept that anything we think we know may well be proven wrong around the next bend, so to speak. In dealing with questions in which we can not hope to fully comprehend, such as the existance of gods or the meaning and purpose of the universe, it is merely expressive of our ignorance to claim that we can know authoritatively any answers to these questions.
Now how does that affect my politics? It leads me to a very libertarian approach on social matters. Personally, I would not commit or endorse abortion on the grounds that it may well be what its detractors claim, the murder of an innocent life. However, I condoned the taking of innocent lives by supporting the various wars over the last decade that I have, from Bosnia to Afghanistan, since I know all to well that innocents are killed in war. I volunteered to be part of the killing machine at 18 and served in it quite willingly and supportively (and still support it today). I supported those wars because in my estimation, the cost was worth the resulting benefits. I might have been wrong but so far, I've not come to that conclusion. I don't know when life starts, or whether we have souls, or are just complex amalgamations of space dust. I may choose not to personally support abortion, but until I have greater knowledge about it, I can not in good conscience prevent someone else from doing since I may well be doing more harm than good as a result of my emotional resistance to the act.
On many issues, I have a similar approach. I have never wanted a prostitute, but I support legalization. I have never smoked a joint, but I support legalization. I have never owned a gun, but I support legalization
That doesn't mean I don't support regulation, though.
Economically, I have drifted from the libertarian perspective, but not on religious grounds. I have merely seen that there are things better done as a society than as individuals. Perhaps it is as some would state, a selfish desire for the highest quality of life, that leads me to this conclusion. But again, this is not a result of my agnosticism, merely a result of a deeper look into economics.