In the long run, we should be able to share toilets (as in using the same toilet, not be in the room at the same time) rather than deeming that men/boys are too disgusting for women/girls to ever use the same facilities. That’s very regressive and will never break down gender stereotypes.
The trouble is that there's what's ideal - where we want to be, and where we are now, and right now, for whatever reason, boys (and men) make a state of their toilets. Ideally, yes, men and boys would be able to not get pee everywhere, and we need a plan to get there, but I don't think having girls clean up after them so they can sit down is a plan - it's just letting the girls do the cleaning and that is regressive.
Personally I think that it's actually that we've socialised boys to stand up to wee, so it's physics, not nature
. DP often sits, and DS1 sometimes does whereas DS2, despite being a bit short, is too enamoured with his penis to even think about sitting down. As a result, DS2 often leaves nasty surprises (which he is called to clean - but still, there's going to be some I miss) - whereas DP and DS1 are fairly pleasant to share a toilet with.