Leaving aside whether this'd be a good policy for a conference, this argument doesn't really check out for me.

You can exchange ideas without making judgements on other ideas. Like, let your ideas speak for themselves, marketplace of ideas etc, or even make comparisons without saying your ideas are _better or worse_ than other ideas.

I'm sure you wouldn't run out of useful and engaging conference content even with some hypothetical arbitrary rules like "don't say idea X is bad", "don't say person X is wrong about idea Y", like, at worst you'd have to make some minor edits to your slides and reword things to be less personal, unless your entire gimmick is that your presentation is a callout post.