I presume you're asking why it SHOULD be illegal. (Clearly one reason it actually is is that most of society is horrified by the idea.)
False. Not that most of [WEIRD] society is horrified by the idea, but that that's one reason why "it's" now illegal. First of all, what is the "it" we're talking about? I guess: marriage before the age of 16 (in most places); presumably, sex before the age of 16 to someone more than two years advanced in age (in most places?). A lot of not-so-free thinkers in WEIRD society come to the conclusion that such a situation would be horrific because they read those sentences and experience a triggered hallucination about all sorts of horrific happenings which they then incorrectly ascribe to those things... but no, that isn't why the things became illegal in the first place. Do some fucking research, Jesus. Naturally, as with any self-reinforcing (although fundamentally misguided) concept, the horrors of unjustified brainwashed anxieties often do play a role when it comes to the maintenance of the ideas that keep them active....
I suspect many professionals would argue that on average, girls would be worse off if it was legalized than if it remains illegal. I have no doubt that they are sincere in that conviction.
Ooh... "professionals". ;)
Your Russian Roulette "analogy"
Comparing marriage to someone you love or sexual contact with that person at the age of 13 to rolling the dice with a revolver and a bullet. (Plus, as Gimmie pointed out, your 97.4% probability is WHACK - but that's not the point.) Wowww. Ladies and gentlemen: we got ourselves a smart cookie.
It was also a different era. We have higher expectations for girls these days -- that they can get an education and make a decision about things like marriage at 18 or older
Those aren't higher expectations - they're different expectations with a caveat that you must put off another aspect of life for a set length of time under the assumption that it's "better" even though it might not actually be better for a given individual.
The radical Youth Rights brigade will now say that total freedom is more important than bad outcomes, and I'm reluctant to get into that argument again.
Mkay, but you're just ignoring the logistics and ethical considerations that inform the position.
It isn't "total freedom versus bad outcomes". It's: "as much freedom as possible to allow for all kinds of personal variation and more efficient ways of locating and addressing any bad outcomes, versus; heavy restrictions on freedom (which of course favors the demographics that aren't restricted), plus Draconianism, plus an oppressive social atmosphere - in place of more efficient ways of locating and addressing the bad outcomes (missing the target more often than not)".
I suppose 6-year-olds should also be free to play Russian roulette.
The "edgy" one-liner looks pretty wimpy when the body falls so short of the conclusion. "You suppose?" Okay. No one else is supposing that.