Not sure where to start with this, rounding your back is actually not that detrimental assuming everything else in the lift is done correctly, claiming he’ll damage his neck from a rounded back is nonsense, if you lift your neck up and keep it straight during a deadlift you can avoid injury entirely, it’s looking down to the ground whilst deadlifiting that can cause neck issues.
I’m not sure where you’ve been training but I have never, ever seen people mocked for being overweight at any gym I’ve visited. The real truth with extremely overweight people exercising is that losing and gaining weight are around 80% diet and 20% exercise, spending an hour on a cross trainer will burn a lot of calories but it will never, ever offset terrible eating patterns and habits regardless of how perfect your lifts are. This is why so called toxic fitness culture focuses so much on fad diets.
When I see someone in my gym that is extremely overweight without a PT with them I know they generally won’t stay around for long, throwing exercise at an eating problem is like trying to stop a wildfire with a super soaker.
As for the comments about self-surveillance and shame, shame is completely natural and not the enemy, when I look in the mirror I’m always looking to improve what I’ve got, shame is part of that equation but there needs to be abundant amounts of body positivity to compliment it, remind yourself of where you started, what you like rather than obsessing on the negatives and shame can be a useful tool.