…in other words, is anything in the world “exempt” from critique?

Lately, I have been reminded of a Penny Arcade comic (disclaimer–I don’t regularly read this comic, but I like this particular one): http://www.penny-arcade.com/comic/2004/3/24/

Kind of a funny example, but what do you guys think? Is anything anyone puts out there fair game? I mean, it’s not like we can stop someone from having an opinion (or even expressing that opinion, for the most part).