yekke2, my first reaction mirrored yours. But then I remembered an excellent point that was brought up by none other than yourself:
I was, once upon the time, of the opinion that 2 Kosher Eidim would be necessary to convict any molester of wrongdoing. I asked a Rav (who was involved in the investigation regarding another Rav who was accused of halachic misconduct) how they could accept testimony of women. He rightly pointed out that we are not trying to kill the man, nor are we trying to give him Malkus or to force monetary compensation. The only shailah was in ????? ???? ??? (in that particular scenario, where even according to the allegations, he had legally done nothing wrong, but was not fit to be a Rav), and for that, 2 ???? are not required.
In hilchos loshon hara, I believe one is supposed to let others know about any realistic chance that somebody is out to do them harm. This person is not supposed to fully believe you, but they are allowed to take steps to prevent any possible harm to themselves.
I think that this idea should fall into that category. (Although I also think awareness and prevention should be the focus here, not shaming.)