First of all, they're doing it publicly and not through the law. Second of all, in vast majority of cases they offer absolutely no definitive proof. Hardly any of the accused have been prosecuted yet their lives are ruined. Any woman can cry rape and ruin a mans life with a half decent story.
And about this case - Ronaldo has already paid her almost 400k years ago. To me it smells like she's blown the money and needs another payoff. Even if what he did was true, she had the chance to prosecute at the time. She chose a payoff instead. Don't come back a decade later, by the time you've probably spent all that money and try to come after him again. You had two options; take the payoff or prosecute. She made her pick.
And what does Ronaldo feeling like a slave in 2009 have to do with this case or his character? Zero
For the latter point, it says quite a lot about his character. He was already earnings millions but called himself a slave as his then club were not allowing him to transfer to Real Madrid. It showed him to be entitled and very self-absorbed. I don't believe him to be that person now, but I think having that sort of attitude at the time the alleged event took place is quite relevant to the case.
Also if Ronaldo paid her off, then that does suggest he has something to hide. If not, then why pay her off at all? In any regards, the mental effects of sexual assault are typically so traumatic victims don't exactly recall reliving it, as you would have to do in court. This is why many cases are reported much later or not at all. Has she asked for more money? It doesn't seem like that is her goal here.
But the line 'ruin a man's life' just stinks. It reminds me off an old Bojack Horseman episode. The allegations are not proven - yet, but they may well be in time (equally they may not). You criticise people for assuming guilt prematurely but you appear to be assuming innocence on the basis its a claim against a famous person so the claimant must only be doing it for attention or money - which is equally as farcical.