Aye. I agree with most of what you said, Rainman.
My kids (and myself included to a lesser degree once reaching adulthood lol) fixate on certain things and the reactions of their family seem to influence the fixation not a single bit.

I try to live by the standard of "choose your battles wisely". If what my kids do isn't harting themselves or someone else and it's a matter of opinion and such, I'll let most things slide. My son KNOWS how I feel about magic and associated subjects and he pushes the line to test his limits (as all children do). Some of what I see I pretend I don't. I never even knew the symbols were drawn on the walls, floors, furniture until we moved to the farm and I started rearranging things.

The house was so thoroughly trashed, though, a den of demons could have easily inhabited the place lol *sigh/sob* So my kids didn't mind adding to the destruction. They don't normally draw anything on inappropriate surfaces, but once the modular reached a certain level of ?? filth they no longer cared.
So I no longer have that problem at the Farm and neither do I suspect I will come to have it once they come home. They also drew heartagrams, faces, and tagged the modular so it wasn't JUST pentagrams.

I agree that when I don't blow gasket over trivial matters, the matters tend to blow over much quicker. But my own conscience and religious integrity wont allow me ignore the symbol or allow it in my home in any form.
So we'll continue to butt heads over it. I just keep reminding him that he only has 1 year and 2 months before he turns 18 and then he can move out and draw whatever he wants