Perhaps if I rephrased my sentence to "doesn't appear to directly contribute to thoughts that normalizes pedophilia" instead of threats to society in general would have been clearer but such a provocative statement seemed too specific and I thought it was implied. My apologies for being unclear with my point. Of course, as you say on this matter, it's people's reactions to art that can be threatening not the inert object itself.No painting has the power to destabilize society. It is merely there and you can always walk away from viewing that work if you find it appropriate to do so. It's perfectly reasonable to see where the concerns of the petition are coming from and agree that the work should not be outright destroyed.
But, the MET owes it to themselves to add a plaque to contextualize the artwork because context is everything in a museum; that is why curators choose works that are thematically or stylistically consistent with one another to display. A curator should strive to select pieces that work towards a greater whole in evoking a specific feeling or discussion.
Clearly, the sexually charged Balthus piece when taken as a whole was not working towards a greater discussion on the sexual objectification of the female body and how a person's view can lead to repressive thought processes. Displaying works of art together that have no thematic ties is the equivalent of putting in pandering fetishitic female character designs in a video game and calling it a deconstruction of objectified female character design.
The rest of what you're saying seems unrelated to the petition which is only asking for a small contextualization. But to address some of what you're saying, the article says there was an exhibit of the artist's work involving Cats and Girls in 2013. It appears that the exhibit ended but the piece is still being displayed as part of their general collection. Displaying it may have other valid reasons than what you're suggesting.
I do agree with the spirit of what you're saying about video game depictions and I may join in that discussion in the appropriate thread once I have full membership.