I've never actually seen the tackle and I wasn't old enough to remember it happening at the time (I'm not an old twat, you see). I can confirm though, that this hatred of him seems to be passed down from other Blades. It's almost unanimous.
The only thing I can really relate it to was the Sordell challenge on Coutts and even though that didn't end his career, I think it's certainly affected it. I think Sordell was a bit of a twat for doing it, more because it was a lazy challenge. I'm not too sure what the aftermath was between the two so I can't really comment on that but I think even then I dont think I'd have the same animosity towards him as some do for Ainsworth.
I probably dont really appreciate how well Dane Whitehouse was thought of at United, mainly because I don't remember him playing but if I imagine it happening to someone like Billy Sharp then it kind of begins to make sense.
When I'm told someone is a twat because of something that happened that I can't remember, I usually dismiss it and make my own judgement but the odd thing is with Ainsworth, I find that really difficult simply because how unanimous the opinion of him is amongst Blades fans.