This comes up regularly.
I wouldn't say it was "most" but a sizable amount. I think the first few responses set the scene. If the first few are cruel, many of the following responses will be cruel.
I was on the end of this recently. I broke my arm about a month back. It was in a cast for a week. A few days later, I went to the High rd to use the ATM. I caught a bus back, and as a) I was in pain and b) i was struggling to negotiate moving around a moving bus with one arm while trying simultaneously to support my bad arm from being bashed I sat in a priority seat. I initially wrongly described it as a disabled seat. A slightly older lady was sitting next to me, then a much older lady got on. I felt bad about sitting in the priority seat but the other lady offered her the seat.
While I got a fair amount of support, the amount of nasty, horrible posts was awful. I got slated for describing my injury as a temporary disability, as disability can only be permanent or not at all and I had insulted all those with a permanent disability. The older lady could have fallen over and broken her hip , which would have been far more serious than me falling and that falling on a recently broken arm would not hurt at all. In fact a broken arm was just an "ouchie" and shouldn't stop doing anything. I shouldn't have been on the bus in the first place apparently and should have walked home as I mentioned it was a short journey (it was about 1.5 miles.) I was personally preventing MNers with a serious disability accessing the seat (even though I doubt they were on the exact same bus at the same time. It was relentless.
Meanwhile, back in the real world, I have found that once it is obvious you have an injury and are suffering/in pain, the vast majority of people are more than happy to help. Like today for instance. Although it was 4 weeks ago, I was in severe pain and was unable to do things with my arm I could do yesterday.. I was getting severe cramp like pain in my broken arm and couldn't lift anything at all with my left arm as a result of the pain. I had a fracture clinic appointment this am. The doctor said the arm was healing well and the pain was due to me using my muscles which have been inactive for the past month. On my way home from the hospital I stopped off at Pret for lunch. Seeing me struggle to get my purchases on the counter, and the debit card from my purse, and the assistant said she bring it to my table. I had one of their lovely popcorn bars but the pain in my arm meant I couldn't open it, so I asked the lady sitting next to me if she could help, again no problem. I bet those kicking me when I was done are not so horrible irl. At least I hope not, and that if someone with their arm in a sling asked them to open something I bet they would, because irl most people are kind. But put them behind a keyboard and they're totally different.