I'm sure it was implicit in Jeff's response, but "bashing" posters isn't allowed around here. Civil and constructive disagreements are welcome.
As for bashing players... So long as it's on-topic, criticizing players for their play is fine, and should be expected. There's nothing disloyal about criticizing a Celtic, even if he's a fan-favorite to others.
Where I think things get tedious is when people use any opportunity they can to bash a player, whether or not it's relevant to the topic at hand.