This internet version of centrism that everyone hates on is bizarre to me, for the reasons you say - the "only commit half a genocide" type of centrism. Are there people who really strike a middle ground on every issue on principle?
I always understood centrism as "I hold enough opinions from both parties that I don't align with either one", which honestly fits me pretty well. I still have strong opinions on individual issues though...
I can see that, you make a fair point. Centrists are probably the least homogenous group by definition, so they don't really stand for anything in particular and the label loses meaning.
However, I do think there is something to be said for using the centrist label to dodge around people trying to pigeonhole you into a specific viewpoint. For example, I've had great discussions with someone about UBI and socialized healthcare before, only for them to feel utterly betrayed and revolted by my stance on gun control (as they naturally assumed the rest of my views would align with theirs along their party lines).
Our political culture is so incredibly hateful and polarized at this point in time that I feel like 'adopting the role of a D or an R' for a single discussion is a recipe for disaster. If there's anything people instinctively hate worse than an enemy, it's a traitor.