On one hand I agree, you are right about our ridiculous nudity taboos. On the other, does it matter whether its clothed or not? The intention of this sort of posting is clearly malicious. Yes its silly that people get treated badly for being seen nude, yes its stupid that anybody cares, but, if it were actually the case that being nude wasn't such a taboo, then forums like this wouldn't exist.
To put it another way, I don't particularly care if someone wants to walk out his house and down the street as nude as the day he was born. I wouldn't personally treat him any different from anyone else.
Yet, I still am bothered by someone who would walk up to people in a park; open his trench coat and force his nakedness on others. It isn't really the same thing as just being naked or being seen naked.
Similarly, there is a difference between posting pics with permission, of which there is no shortage out there, and posting something you know you wouldn't get permission for. They really are two very different act, even though they are technically the same actions.
And yes, its nudity taboos that give power to the action and we need to get over them, but, we also don't need to coddle the petty assholes who don't think consent matters.