If you as the maintainer said "hey, I don't really care about Free Software, I just think this is a fun/useful project and the GPL 3.0 meets my needs." and people still bugged you about Discord, I agree you should probably just tell them to fuck off. They might still try to get you on board with Free Software in the first place, but it wouldn't make sense to bother you about details like a chat program if/while you don't care about the cause.

However if you said "I'm creating this project because I care about user freedom" someone might point out "Great. Well, since we're on the same page as far as user freedom, let's take a look at the tools we're using..."