Maybe there are public places that our society should restrict to those who physically have or do not have a penis. I don't know, but seriously, if a penis having person who feels like a woman needs to pee, and they feel more comfortable using a woman's restroom, who cares?
I have been sharing public restrooms with other penis owners for my entire life and I can't really recall ever actually seeing a penis other than mine in one.
I also have two young sons. It is entirely possible that someone with a penis might try to do something inappropriate in one of these restrooms and still be in the proper restroom for their biological sex. It is something that every parent must consider and I don't think that the presence of a transgender person in a restroom elevates that risk at all.
Of coarse, it is possible that a transgender person might do something terrible in a public restroom, just as it is possible that a Muslim might be a terrorist, or a man might be a chauvinist. We should probably stick to condemning the behavior and not the entire class of people.
I suspect that folks like C. C. are really just upset about the growing acceptance of a group of people who they hold underling prejudices against.