I think it is even more fundamental than that. I believe that the fundamental issue is one of anthropology - what is man (and woman). And, even before that, Who is God. Let's leave the definition of God out of this discussion (for now). I want to discuss anthropology as it relates to what men and women are.
On the conservative side of things (both politically and theologically) we tend to believe that man was created good but is fallen. Thus, we tend to think of man, in his natural state, as a "twisted" individual. We may want to do good and to be good, but we lack the ability to do so. We are so bent by our sin that we don't even know what is good anymore. Thus, we need an external source to help us know and understand what God desires from us. We identify with Paul in Roman's 7
I know that nothing good lives in me, that is, in my sinful nature. For I
have the desire to do what is good, but I cannot carry it our. For what I
do is not the good I want to do; no, the evil I do not want to do - this I keep
on doing. (Rom 7:18, 19)
Thus, our natural state is one of brokenness and the inability to do good. Our natural state is one of separation from God. For this reason, God became man in the person of Jesus Christ so that we (and all creation) might be redeemed and be united to God by God's grace. In the conservatives eyes, mankind needs to die so it can be reborn. We've marred God's image and lost His likeness by our sinful actions.
On the other hand, most progressives I've known tend to think that man is basically good. Our natural state is one of blessedness. They like to speak of "Original Blessing" not "Original Sin." They believe that most people want to do the good and, if we just educate them enough, they will choose the good. Mankind needs fixing, not re-creation. Man still has a lot of the image of God and still bears His likeness.
That is an oversimplification, of course, but I find it to be true to a large extent.
So, how does this play out? In terms of the sexuality debate, the conservatives see homosexual orientation as a consequence of our fallen nature. Progressives see homosexual orientation as a natural occurrence and, therefore, a moral good or moral neutral. In terms of Evangelism, the conservative see other faiths as not participating in the new creation that all men need. Progressives see that all faiths as expressions of man's quest for God and, thus, evangelism is not as necessary.
So, which is it? Is mankind basically sinful and fallen (and thus with a need to die to self and be raised to new life) or is mankind basically good (and thus needs only education and improvement)?