I once believed that, in a discussion or debate, you should settle on mutually agreed upon definitions from the get go and then present arguments using those definitions. Unfortunately, it seems like a lot of people would rather spend their time saying "YOU ARE USING THE WRONG DEFINITION OF THIS WORD" because, I suspect, they realize that if we removed the implicit connotations of the words they used and just used the definitions they wanted, their claims would look pretty weak.
I don't necessarily disagree. However I think it's a less calculated move to do so by your average American, and more an emotional move. They don't necessarily understand the terms they're engaging but they know enough and feel enough passion to recast it according to their needs. They honestly believe they're being discriminated against, regardless of whether the evidence supports it or not. And so in their minds, they own the word just as effectively as a black person who can actually trace their roots back to slave times.
I think it was the emphasis on subjectivism that's been a mainstay of liberal political discourse, since I was in high school at least, that some conservative thinker finally looked at and went "Wait a second. I can totally use this for my own purposes and thwart their's at the same time." From there, average folks clued into doing the same thing. And so we've arrived at Donald Trump, who can say what he wants and use words as he sees fit and the rest of the world is just left gawping in shock that he has the temerity to do so.
I think it kind of illustrates the danger in using/misusing powerful words carelessly. Words like "racist" and "bigot" and "sexist" have very strong negative connotations, so people like to use them as weapons to attack opponents. But when you overuse them or, worse, use them against basically innocent people who just happen to be in your way, the words begin to lose effectiveness and unfortunately so does the emotional reaction against the negative things those words represent.
Basically, every time someone is called a racist (or someone they know/respect strongly is called a racist), they either say "Wait a minute, I'm not a racist but I'm being called a racist, is it possible that other people accused of being racist are actually just victims of smearing?" or, worse, "Well I'm a decent person and apparently I'm a racist so I guess racism isn't so bad". Eventually this reaches a tipping point where people that are either immune to or embrace the accusation exist in sufficient numbers to actually start hitting back, hence you get Trump saying whatever he wants with seemingly no consequences. I know a lot of people that do this aren't intentionally being dishonest, but this is the conclusion of slowly destroying the meaning of a powerful word.
Something similar happened to "socialism" and "communism" too, since the Soviet Union is old news and Republicans seem to just call everyone they don't like a Communist. Naturally, the logical conclusion of that is Bernie Sanders nearly winning the Democratic nomination as an avowed Socialist (despite really being more like a social democrat).
It's a bit like using antibiotics. In moderation and used in the right situation, you kill the bacteria. Used in excess, you get a superbug that laughs at your pitiful drugs and kills hospital patients.