It's pretty strange to me that the very act of non-lascivious public nudity would be illegal. In more liberal parts of the world(and I would've guessed Portland), this sort of protest is considered protected speech.
The relevant bit there:
We read the challenged ordinance as focusing on the goal of regulating conduct which the city council has determined to be injurious to health, safety and morals, i.e., the prohibition of public nudity or indecent exposure not intended as a protected symbolic or communicative act. Id. at 82.
In other words, the court specifically acknowledged an exception to the ordinance in order to protect symbolic or communicative acts (the other alternative would have been to declare the entire ordinance unconstitutional, as it's fairly well established that no-exception bans on public nudity violate the first amendment), which this clearly was, so he should be fine.
Of course, all bets are off since this happened in an airport, because terrorism.
I think might even be bad for children NOT to see naked people. It could indeed have a bad effect on them, I think, e.g. cause self-confidence issues when they grow up, because they wouldn't know what things are going to be like, if it's normal etc. Moreover, it allows for creation of totally unrealistic, photoshopped beauty ideals, because children/teens see (nearly) naked people mostly in some kind of highly altered adverts. Seeing the real thing brings them down to earth...
This happens in locker rooms here as well. How else do you change out of your swimming trunks?