I have "retard" in the same category that I have "fag" and "nigger" - offensive. That's really weird for me, because I'm an incredibly vulgar person (I don't blink at "cunt" - my own hypocrisy, I'm sure). I wrote an article on "word re-appropriation" which is the process of repossessing a word (the most notable one I can think of is "queer" - another word I still detest). I think it's an overall useless objective: any word can be used offensively, trying to redefine the word isn't going to change what the people using it intend it to mean. As for the word "retarded" in general: I don't use it, and I cringe when people do use it. Why? I don't know, exactly. I have a distant cousin who's pretty severely handicapped - perhaps seeing some of his life has made me a bit more sensitive to it. Perhaps it was my High School Accounting Teacher, who was stoically against the word as her brother had a mental deficiency (her brother being one of the nicest people I know). I don't know if I have a solid reason for not liking that word. With "fag" and "queer" and "homo" I have a solid reason: I'm gay, and I find them very offensive. (Though, that begs the question, do you have to qualify for an adjective to find it offensive (I don't think so)?) --- As for tumblr: I don't consider tumblr "social justice" - I consider it, instead, the fetish-izing of ultra sensitivity. I find the tumblr group particularly annoying because they (using that term very generally) never seem to actually care, they only care because they're told they should. That, and they go far, far, overboard. For instance, on reddit I was called out for committing "trans erasure" because I thought the institutionalization of the word "xe" was idiotic. The same person later said, "Fine, then I don't respect your decision to call yourself gay." That's just ridiculous. They're unable to discourse in any respectable matter, and I think that's why tumblr gets a very bad wrap. --- Side note: I'm familiar with JonTron, and have always found him extremely annoying (DYKG is at least bearable, thankfully). None of this is surprising.
Not to split hairs here, but gay people and black people might not see with you on this one eye to eye. Not sure anyone has ever been lynched to cries of "retard," and I'm positive that "retard bashing" is not a thing. I don't think the word retard belongs in the same category as "nigger" or "fag." Frankly implying such a thing is more offensive than the words themselves.
I disagree. Plenty of people with mental handicaps have been beaten and murdered for it. Just a few sources. It doesn't get reported as much as violence against gays (a group I fall into) and blacks, (cynical moment: probably because it's not as 'sexy' for news media), but it's definitely there, and it always has been - all throughout history. Don't forget the Nazi practice throughout their reign of executing those with mental handicaps and birth defects (Nazi Germany wasn't anywhere near or the last nation to do this, but it's probably the most well known). It does belong in the same category, I think.