Open debate doesn't need to include stating, without context, that your debate partner is a danger to children. That's not dissent. It's not debate. That's character assassination. That's slander.

It is entirely possible for verbal viciousness to overwhelm any actual debate. I am frankly rather horrified that you chose this as an example, and can only hope that you either didn't read the tweet carefully, or didn't take the time to imagine the apparent meaning to a neutral observer.