I don't agree with "if I don't perpetrate this harm, someone else will, so it's okay" because that pattern can be used to justify any harm. If I don't perpetrate this harm, and someone else does, the moral culpability rests with them and not me; and that makes all the difference.

I'm saying that doing business with people who oppose abortion isn't the perpetration of harm. We as a society do not economically ostracize people who hold a pro-life position. There is no need for some random software developers of some groupware to be doing that.

We don't? Sure we do. We boycott all sorts of things. Economics and market relationships are one of the most potent tools people in our capitalist society have for effecting change.