And okay, a tiny fraction of the time people are just trying to use words as a Schelling fence.

I'm not sure it's that tiny, especially once you're using the "steel man" version of the arguments; i.e. things like "Schelling fences" do not often appear in the reasons given for the disagreement, but that can still be what it boils down to.

People who object to abortion may be objecting to a weakening of the social stigma against the murder of innocents - that social stigma performs a useful function in society, so allowing anything that could be described as "murder of innocents" is perceived as bad, regardless of whether that thing is in itself bad.

In other words, even if words are hidden inferences with leaky generalizations etc. - social norms are still defined in terms of words, and so "pointless" debates over definitions still have their place in discussions of morality. Questions that shouldn't be morally relevant ("is abortion murder?") become so because of the instrumental value of social norms.

So yes, sometimes pulling out a dictionary in the middle of a moral argument may be justified. The discussion can then turn to something more useful, like "is it worse if the norm against murder is slightly weakened, or if women have to keep children they don't want?".