I think so, on all four counts.I think the main reason is conflating sexual attraction and sexual behavior. Any inappropriate sexual behavior should not be condoned in the BSA (or anywhere else). But one should not assume that a gay boy who wants to join the boy scouts does so because he is a sexual predator. This is incorrect.
There are probably other reasons as well, such as the belief that any and all attempts at equality for gay people are part of a nefarious, anti-religious, secular gay agenda. I believe this is wrong as well.
A third reason is the perpetual fear some people have of anything relative to gayness, especially when it concerns children. People are afraid that their straight child will either be sexually molested or sexually indoctrinated by gay boys into believing that being gay is simply an alternative lifestyle. This is contrary to Church teaching. I think, however, that fear is misguided. If anything, it is most likely the gay boys who have more to fear in that if other boys perceive they are gay, they may become the target of ridicule.
Finally, there is the whole macho issue. I would bet that more men are opposed to this change in the BSA policy than women.
A lot of the opposition to SSA boys in the Scouts doesn’t seem to be based on principles, or notions of fairness.
It seems to be either:
(1) SSA boys are predators, or are going to “turn other boys gay” ((1) and (3) above);
(2) “These people” and their “gay agenda,” that is, if they support something, it must be wrong ((2) above);
(3) The fact that some people just plain don’t like gays, based on their childhood or teenage experience (“See, guys, don’t make fun of me for being gay! I’m not gay! In fact I hate gays just like you do!”) ((4) above). I grew up with plenty of that.