What would be the harm?

[The Grand Nudger]

All that matter is whether there is a selective pressure against it or not.  People who belong to societies where such things are accepted do not prosper as well as societies where such behavior is not tolerated.  If the society suffers, so do the individuals.  If the society benefits, so do its individuals.  As they say, a rising tide floats all boats.  It has nothing to do with reasoning toward it being in one's interest.  So, no, you're simply wrong about it not being a biologically based impulse.  It most definitely is.

Evo bio doesn't care about societies prospering, either.  

I don't know what your point about mooring morality to its evolutionary roots is, you're not particularly clear here.  Moreover, for someone who takes harm as the objective basis of morality, I find this a rather strange position to take, as it seems to undermine your contention that harm is an objective moral standard.  The moral standard of harm is quite obviously tied to biological interests.  Have I misunderstood you?

Harm is an objective moral standard because it can be quantified.  It can be observed and demonstrated.  Things being in the periphery of biological interests doesn't mean that their basis -is- a biological interest.  

The only interface evolutionary biology has with ethical objectivity is in whether or not it provided us with the apparatus to make objective assessments.  It may not have done so (I'd say certainly didn't do so)  for the purposes of making moral assessments..but so long as it provided a meaningful apparatus capable of both noting and forming an objective proposition then it doesn't matter much that this ability was originally there to help us find lunch and it certainly doesn't mean that this objective proposition is lunch based.  

Is it true that good and bad have some reference to harm?  Yes.  Can harm be demonstrated, and thus shown to be some true fact of a matter x.  Yes.  

That these facts of the matter sometimes align with our biological interests is fortunate, but it's also possible for them to be in contradiction to those interests or to the thing which they evolved in pursuit of.  Doing the right thing can be disadvantageous to you.  Doing what is natural for you, can be wrong. Sometimes, the way you find your lunch can be the worst possible thing to do..ethically speaking, on basis of harm.

I'll reiterate that while you are seeking to tie moral objectivity explicitly to biology, that is very literally the last thing that moral objectivists want to do. That's why I mentioned that you tied yourself into a knot, earlier.