The whole 'people shouldn't challenge others' about their use of anything... only really works if other people try not to inconvenience folk by using facilities they do not actually need.
So I won't question someone using the disabled toilets or the lift when its super busy... but you won't use those things if you don't actually need to.
As soon as either side of that social contract breaks down, people get challenged and feel bad, and people are inconvenienced.
Having sat in front of lifts in such a way as to not block people getting out, and having had numerous faster to move, able bodied people shove in front of me, making me wait for lift after lift... it does really start to get on my tits, I have to say. And no I cannot just whisk my chair in in front of them, that would risk breaking someones leg given how big and heavy it is and how unobservant people are about their surroundings!
I have also had people cram in the lift after me putting the lift over its weight limit (my chair = 2 people, plus me, so the fact you can physically cram another three or four humans in does not make it ok, if the lift says 5 people and its now containing 7 or 8, it will not work. Then I get glared at of course!
Or, here's a fun one - someones arse is in danger of touching my controller. I could stick my hand in the way, so now my hand is touching a strangers arse, or I could let their arse drive my chair into the person next to us. Either way, I'm getting the blame. So I turn my chair off. But it takes a few seconds to fire up again when I switch it on, so NOW im getting glared at and tutted at for taking a while to get out the lift - into the crowd of people waiting to get in, who assume everyone in the lift is able bodied of course, who all take umbrage at having to shift their arses out of the way and potentially lose their spot in the queue (and woe betide a wheelchair user wanting to come the other way, t hey have to back up to let me out and then a flood of people charge in and the other wheelchair users lost their spot!).
It's just a lift eh. No big deal.