I think people who say this are generally not commenting on pedators, but on the idea that it is uncomfortable to be naked in a place where someone might be thinking about you sexually.
And that is an argument people have made at times, that they don't want someone they don't know thinking about their nudity sexually, even if they never know about it. Many people would feel somewhat or even very uncomfortable if we found out that some person we'd met casually was wanking off thinking about them in private. Others it wouldn't bother at all.
So on the one hand about why that makes people uncomfortable, and why on the other hand we tend to say that fantasies are fine as long as we keep them private. There is a bit of a "don't ask don't tell" element
My own sense is that in general, the preference not to be nude with opposite sex people isn't really about safety or even sexual desire, though those things are real. Because most women would also not like to change with their brother who they feel safe with and with whom there is no sexual element. But most would not mind changing with a lesbian who might be attracted to us as long as she wasn't behaving in an abnormal way.
It may be worth trying to articulate clearly what that's about because I find even some women, especially younger ones, seem to need a clear explanation before they "get" it. Sometimes people say it's about dignity which I think is true as far as it goes, but the question then is, why do people feel that changing with even a safe opposite sex person in these kinds of settings is undignified?