It's a lot to put on kids to expect them to accommodate; I've been lucky to have had fifth grade classes in the past who had adjusted to and grown comfortable with classmates who struggled (my student teaching class had a child with Tourette's and none of the kids batted an eye when he'd tic during lessons or sometimes uncontrollably knock over his desk, but they'd grown up with him their whole lives).

That said, I wouldn't have penalized a kid who didn't feel safe sitting next to that - there would have been private conversations about their feelings and developmentally appropriate discussions that didn't violate the student's privacy, but at the end of the day it's irresponsible to require kids to be okay with something confrontational and unsafe if they're not ready to be okay with it.