I think asking someone to refrain from speaking (what they believe to be) the truth is one thing, especially if they are doing it simply to cause controversy, draw attention to themselves, or signal some sort of tribal loyalty. If that is what the flagged comment was doing, then perhaps flagging them was the appropriate response.
However, asking someone to actively say something (that they believe to be) false is not within the scope of what I would call "politeness".
For instance, I have friends and acquaintances who have religious beliefs that I do not, and those religious beliefs are essential to their identity. I don't constantly tell them that they are deluded idol worshipers (that's rude). However, I don't participate in their observances and I don't hide my disagreement when the subject comes up.
However, asking someone to actively say something (that they believe to be) false is not within the scope of what I would call "politeness".
For instance, I have friends and acquaintances who have religious beliefs that I do not, and those religious beliefs are essential to their identity. I don't constantly tell them that they are deluded idol worshipers (that's rude). However, I don't participate in their observances and I don't hide my disagreement when the subject comes up.