But you can't know. Not by looking at them. Sensible thing to do is not allow men into situations where girls and women are vulnerable. Why don't you get this?
Women and children are always vulnerable, but not all men are bad. Do you honestly think that bathrooms are inherently higher risk places than say any of the other places people get sexually assaulted?
You see this is the problem - if you equate homosexuality, transgender etc with something inherently bad / wrong, then yes I see your point. Keep the bad people away from women and kids. But here's the small teensy weensy problem with that - gay, trans, rest of the alphabet people are not inherently bad people just waiting for an opportunity in a bathroom to leap on some unsuspecting person and assault them.
This is where I get so upset with the whole lib/conservative paradigm we always find ourselves in in these discussions. Here's a newsflash for everyone on BOTH sides - the world ain't black and white. It's finely nuanced shades of grey ... all the way.
So back to the trans issue - they suffer even worse hatred, bullying, prejudice etc than gay people do (and that's bad enough) plus they have all the body dysphoria issue because of their situation - so when they finally have the courage to dress how they feel so that the outside matches their belief system - they would like to a. be able to go to the bathroom that matches how they present and b. do so without incurring further hatred, prejudices, etc. This is not an unreasonable request.
I presume if someone came to you and said - every time I go to the bathroom I face prejudice and discrimination and I would just like to be able to go pee in peace and safety, you wouldn't be so hardhearted and indifferent to their problem that you would refuse them the right to have a place to pee.
Now that has to be balanced against the fact that not everyone wishes to see other people's genitals, especially not if the genitals are different from the sign on the door. A desire which is also very fair and reasonable. So the solution lies in accommodating both requirements. A decidedly difficult task!
When you start throwing total bullshit into the mix about kids have to be kept safe from predators with the clear implied meaning that gay / trans / etc etc etc are the perverts that the kids need to be kept safe from you lose the plot completely, and just expose your intolerance and prejudice which started the whole problem in the first place - i.e. it was intolerant folks and their prejudices that made the bathroom unsafe for the people you now want to exclude and discriminate against even more ..
As to the question of sexual predators - again, unless you are going to lock up every person on the planet because they 'might' do something - we judge people on their behaviour, like this Yaniv person. He exhibits every textbook behaviour of a sexual predator with fetishes, and pretty much zero behaviour of a person with gender issues. He is a man who is very clear in his own mind about what he wants, and how he is going to get it. The whole crossdressing thing may also be a part of his fetishist fantasy, although I suspect it is simply a means to an end. Sexual predators will play any role that gets them close to their preferred targets.