What I took to be Wayfinder's point was not that all people are selfish to great degree, but that we largely tend to be that selfish in today's world.
What this essentially translates into is that there are no shortage of people who are so self-centered that they will not attempt to submit to the sensibilities of those around them where such consideration wouldn't cost them much of anything except a bit of thoughtfulness.
In fact, some are so self-centered, they will actively antagonize others simply for the sick pleasure of doing so, since their own entertainment comes before that of even the sim as a whole.
I don't think it was his point that EVERYBODY is like that, because there are plenty of people who show consideration for others.
A PG environment is one which is defined by the people in the environment making every effort to avoid using references to things which would be deemed offensive or vulgar in general, including written, auditory, and visual cues.
And I for one am thankful that such areas exist, because not all adults prefer the often cruder environment of Mature environments, and enjoy being able to hang out and interact in places where they don't have to worry as much about offensive material. Call them prudish if you will, but that is their decision, their culture if you will.
And I think that in all practicality, it is the sim owners who decide what constitutes the acceptable from the unacceptable, with input from the sim patrons.