Because you made it sound, in the way you posted, that you took the toy away  from a little kid because a grown man didn't show the proper respect for a fictional character.

Your words were (emphasis mine):

 "She was bored,"
said my friend, "so I gave her Aquaman to play with. He doesn't matter."

His exact words, burned into my brain. I took the toy from the child* and
replaced it on the shelf. "Does to me," I said.

If you had said " I wish you'd have asked first, or "these are special to me I would rather you didn't let her play with them" It would have sounded a lot different .

They way you stated it, makes you sound like you punished her for something her father did.

And please don't get me wrong. I do have a policy of not letting folks play with my figures that I have on display. Over the years I've had people break, and ruin several items that meant a lot to me, so now it's strictly hands off unless you ask, and most likely I'll hold the figure, or statue or whatever, while you look at it. So I can see why you might not want kids messing with your figures.

For friends with children, I have a big ol' box of "regular" action figures and toys to play with, and they can do whatever they want with them.