Religion is a poor source of morality

[Esquilax]

But again that is all speculation on your part. I could also say that empathy is a reproductive disadvantage leaving compassionate people vulnerable to hostile groups.

Yep. What, did you think evolution was this perfect, flawless series of utterly advantageous mutations? It's more than a binary good/bad decision: some mutations are absolutely brilliant for certain things while giving their organism crippling flaws in other areas. For example, our upright gait opened the door to a lot of advancements that led to us becoming the dominant species on the planet, but at the same time the specific configuration of nerves and structure in our upright backs leaves us vulnerable to a quite astonishing array of back pains, injuries and deformities because much of the architecture back there is still set up for forward sloping quadrupedal motion. All that a given mutation needs is to confer a net advantage to be retained within a gene pool, it doesn't need to be advantageous in every possible situation.

It is premature to say with any confidence that any particular evolved trait is primary for moral behavior and I believe there is good reason not to consider natural instinct a reliable moral guide. Virtuous action is often contrary to our natural instinct, like showing courage in the face of danger. You seemed to dismiss revulsion of deviate behavior as socially constructed problems. Could we not also say that social constructs like a sense of duty and honor contribute positively. Again socialization is neutral without reference to a higher standard of value that instinct or cultural norms.

I would say that our natural inclination to empathy informs our morality, rather than being solely responsible for it. There are also other factors that go into it, and I wouldn't even say that empathy is the largest contributor among them. Rationality, from where I'm standing, is far more important; our ability to assess and investigate scenarios allows us to determine their moral dimensions, in which empathy is but one of several lenses we can use to view the scene. We're far better off, morally speaking, when we recognize the importance of understanding consequences, motivations, and the objective facts surrounding any given ethical question.

The thing to remember is that evolution can often have little in the way of nuance, such that the reactions and instincts it instills in us can often be applied inappropriately. With regards to revulsion, that has a benefit in situations where the thing that disgusts us is harmful to us (snakes and spiders can hurt us, and they are commonly associated with revulsion and fear) but that same reaction also causes us to react negatively to things that are not harmful but are enough of an Other to set it off anyway. The thing to do is to recognize that what we're evolved to do does not have to dictate what we ought to do, and to rationally assess what actual harm or benefit the thing that we revile does, so that we have a more objective justification than just subjective animal instinct.