True, it annoys me when characters diss the wardens because I'm a huge fan of the order, and honestly everyone should be kissing their ass
but I guess that's the point. People only appreciate the wardens when they need them, when there's no blight, the wardens are forgotten
Sera has a line of dialogue after Here Lies the Abyss that is probably the most poignant thing anyone has said about hating on wardens. Something along the lines of.
"Normally, a hero shows up after a bad thing happens. Wardens are the other way around, they're the good thing that reminds you a bad thing exists."
So it's probable that most people hating on the wardens don't necessarily hate on the wardens themselves, or on the organization, but rather subconsciously they're being reminded by the existence of grey wardens that the blight is a thing. They want to forget about it, but can't because the wardens won't let anyone forget (for obvious reasons) so some resentment makes sense.
Though I really wish we had gotten DLC where the HoF shows up and can give all the companions talking smack about Grey Wardens a verbal beatdown. Basically break all the Grey Warden secrets and reveal all the most horrifying details about darkspawn. Such as how they are created...