Let’s say you are a white person, and you want to convey that a black person is worth less than you are, that they are unruly and unreliable, that they are violent and deserving of punishment, and that, in general, the state should be able to do to them whatever it deems appropriate?
Well, you used to have a word. You used to be able to use that word because you were in power, and you knew you were in power, and the black people you were discussing were legally chattel. So you could use whatever word you liked and the majority of the people (well, the majority of those who were recognized as people, anyway) would agree with you and not think twice about it.
Then, as time went on, society became a little less white, and you became a little less powerful. With some chagrin, and a lot of vicious underhanded terrorism, you admitted that you were wrong to hold as much power as you did and that you had to share. Sometimes. Eventually you decided that you having more than your fair allotment of everything and sharing sometimes was the same as everyone being equal. You got pretty content with this state of things, because lots of people around you (who were white) agreed with you that the problem was solved, and you still got to enjoy many of the benefits of having the problem (while black people around you were still suffering from the problem).
And then something went wrong. Many people have always been saying no, you having the most and sharing sometimes is not enough, but they started saying it louder. Maybe it was because the agents of social control that you built act mainly on your behalf, and so black people tend to end up dead at their hands. And you needed a reason to dismiss these angry black people, a reason to say they were wrong, and a word to explain how you felt about them.
“Thug” is a very convenient word. It has all the associations of your old word, but (officially) does not have racial connotations. There are white thugs, right? Totally. So you can express all that hate and resentment you feel quite nicely with this new word, which is just broadly-defined enough to give you plausible deniability.
But guess what? There is no plausible deniability for language. Language is a democracy. Meanings are not prescriptive, they are descriptive. So, when you use “thug” to mean “a black guy who makes white folks a little more uncomfortable than they prefer,” no one is confused about what you mean. Except maybe you, doing internal backflips to convince yourself that what you are saying is not a racial epithet—even if you are using it that way, and even if you are conveying exactly the meaning you want to be conveying by using it that way. Even if other people, perhaps just a bit ignorant of what is going on, use it too. Even if there are other meanings.
What I’m saying is, we will not let you off the hook. Because, no matter how much you justify and contort and argue that you are not being racist (and racism isn’t even a thing anyway, you assure us) the rest of us hear what you really mean. We know very well what you are saying, and we want you to stop.