I'm so confused about your point here. Do you think I don't realise that concept of race is nonsense? Do you think that somebody who will discriminate against me or attack me because of the colour of my skin cares about that or has given it an ounce of thought? Do you think I could stop them simply by patiently explaining this to them?

Should I use the construction "somebody who will discriminate against me or attack me because of the colour of my skin" every time I need to talk about this problem? Or substitute it for the well understood English word "racism"?

Pendantry like this is the sole domain of people who get to watch from the sidelines.

And no. George Floyd's murder gained broad attention because he was black and we're living through a time of extremely heightened racial tension (particularly black vs white). If Floyd had been white, however much he'd cried out for his mother, most people wouldn't know his name. Google Tony Timpa for evidence of this.