Do you think you're preventing it with laws?
Do you think that laws that make robbery illegal prevent any robberies at all? Do you think laws against murder prevent any murders? Do you think laws against child labor prevent any children from being given jobs in manufacturing plants? It won't prevent all of them, but it *will* prevent at least some.
Now tackle it from the other direction. First off, be aware that I'm NOT making a comparison, I'm making an ILLUSTRATION OF CONCEPT. And it's chosen specifically because it really hammers home the dynamic at play.
We currently have laws that prevent adults from having sex with children. They don't prevent every single case of adults having sex with children, because at least some - possibly most - people don't want to break the law and don't want to risk being caught.
If we got rid of those laws, and we decriminalized adults having sex with children... do you think the number of instances would stay the same? Or do you think they would increase?
Does someone stand at the front of many or any public restroom asking to see your genitals?
This is dumb. It's annoyingly and shallowly dumb. Some few males can effectively pass as females. But the majority of males who have gone through male puberty to NOT pass, and we don't have to see their junk to be able to tell that they're males.
Eddie Izzard does not pass at all, no matter what skirt they wear, no matter how much makeup they have on. Nobody needs to see their genitals to know that they are male.
We're a sexually dimorphic species, and we're really, really, really good at telling which sex other post-pubescent humans are. For the love of reason, please stop pretending that people's sex is a massive unsolvable mystery. It's not, and you ◊◊◊◊◊◊◊ know it.