You can call it demagoguery all you want, if you're complaining about something like "Wow, the NDP has an ad out calling Trudeau a pretty faced empty suit, corrupt politician who breaks his promises!" you're just describing a political ad that is, for what it's worth, probably true, in the first place. Trying to act like any criticism that doesn't fit your weird tone policed boundaries of the liberals because it could somehow empower other people (like the CPC) is ridiculous. It's a campaign and no party is above criticism.
"When you sound like the CPC you're doing something wrong!" is a dumb boundary because they're not the same and that only serves two purposes: First to try and equate the two parties which are ideologically complete opposites, and secondly to just stop all criticism altogether, which is more or less what happened whenever anyone tried talking about the whole blackface ordeal - anything that could hurt the Liberals is too dangerous for some people to talk about so then there's nothing to talk about.
"Why can't all criticism be calm where we all sit politely at the table" is just a line that defends the status quo.