Using that posters logic, it calls into the question of trademarks for things like the NAACP. If a slur is a disparaging term regardless of it's context, use, or history then this becomes a problem. Similar as well for GLAAD.
Naturally it WON'T ever actually be a problem, but just highlighting the flawed logic that somehow because a word at some point in time was used as a slur and disparaging suddenly means it always is regardless of context or manner of use.
"I am appalled that somebody who is the nominee...would take that kind of position"
"A court took away a presidency"
"...the brother of a man running for president was the governor of the state..."
It's horrifying because Trump is blunt instead of making overt implications.