“Why even take species-groups instead of groups defined by skin color, weight or height? Why single out one property and not others? “
I am not sure if this is accurate answer but I feel like bringing this up: in some cases we should single out some properties over the others based on their function in regards to our interests. Obvious example: separating men and women in combat sports.
Another important detail is that in ideal world we could evaluate everything on case by case basis instead of generalize. So in general it wouldn’t be fair let men and women compete against each other and we should separate them but if we would evaluate every single potential fight, we might find some cases where it would be appropriate and fair to let some man fight against certain well trained women.
Not a great examples and not really criticism, but I think it is but of extensions of ideas that you presented here (which I mostly agree with). It was just something that came to my mind as I was reading this (perhaps because of my martial arts obssesion?) and wasn’t really addressed.
I often use “What are you up to?” as it seems more natural and can be used almost in any context.