I've seen that happen too. When I first had my fan fiction critiqued I 'fought back' then was 'pm'd' and told that wasn't the ettiquette. lol! (On one fan fic place who shall remain nameless I got my account 'blacklisted'* (at least I think that was what was happened as every time since I try to submit a peice it gets 'denied') coz I argued with the mod about her comments on my characterisation of her fave DW character). Since then if I'm given critique in anything I smile politely, nod then [if I don't agree] go away and do what I want.
*yes I know you would never have guessed I was such a rebel...but I was a stroppy teenager at the time, and thus always right.