The rules and enforcement are fine as is.
They have loosened up on this a lot since I got here and any more would be a mistake I think. This rule is one of the things that separates the PG from Sherdog.
IMO, usually "criticism" is acceptable but outright "bashing" is not.
Consider this question when you post something critical KFM:
Is your statement backed up by facts or is it more similar to a conspiracy theory?
I'm not a MOD but that seems to be where they draw the line. Suggesting that you know someone's internal motivations (by suggesting that they threw the fight) seems to cross that line. There are no observable facts to support your opinion because none of us can know what another person is really thinking.
The only way those kinds of statements would be acceptable is if there was evidence of it, like a leaked video or an admission by a fighter or UFC official.
I will say though that I think the PG overreacted by banning Grease-Gate threads back in the day. In that case there was evidence to discuss and it wasn't just some conspiracy.