There are several truths here with the first being the fear of transgender people. The second truth here is one of protection. This plays on the patriarchy of our society. Yet another truth is that these conservative men are rapists themselves. They know they could not trust themselves so why would they trust another man who is becoming a women. Most of this is irrational fear of course, but something that propagandists have cultivated. Also, I am sure there is at least one case of a transgender women doing just this. I understand this is more of a nuanced view but if you are trying to understand why propaganda is effective it is important to realize how it twists the truth.