The thing that makes people not want to hit turtles is that their durability is high, but their threat is low. Whether that durability is high because of HP or AC is rather irrelevant.
People don't empty pistols into actual tanks just because they're easy to hit in the real world. People don't assume that the Hulk is gonna be squishier than Iron Man just because he's not wearing a shirt in a world of heroes.
Likewise, people don't assume that bears are easy to kill just because they have a low AC.