Maybe it would help to bear in mind that the real issue isn't use of the costumes, but what doing that represents and what its aims are. At that level there are light years between this stuff and the use of animal costumes by, for example, rival football teams, the Easter Bunny, and so on.
Berlin's totally perverted sense of things shows up in the other ideas he had for the boy: 1) having sex with him at night in his back yard while his parents slept upstairs, 2) having sex with him in these costumes, 3) trying to get him to have sex with another adult while Berlin watched, 4) his interest in taking photos.
Nobody living can ever stop me
As I go walking my freedom highway.
Nobody living can make me turn back:
This land was made for you and me. (Woody Guthrie)