DA - I don't think they were thinking about the psychology of it (although I get what you mean). But I do see their point RPF in a way objectifying real people* and I think it is one of the main reasons why it makes people uncomfortable.

*Not saying there is anything wrong with it as long as no one is harmed, but it is a complex issue. This is why I believe in cases where actors have spoken against it (most of the ones I have read about have been about roleplaying, but fanfiction will fall under it too) people should respect it.