That's the standard gay talking point, but the truth is that only gays are a sexual threat to boys. It's like letting an adult heterosexual men lead a group of girl scouts.
The other thing is that the boy scouts includes teenage boys not just young children and gays are definitely attracted to teenage boys. How do I know, well here's a photo of a well known professional gay who's made a living by being attractive to gay men. Seems the teenage boy look turns on a lot of gay men.