I personally don't like anything like that coming from an anonymous source. I've said this before on threads.
What are you referring to, if you're not a BS. What is it you don't not like coming from an anonymous source?
It's entirely understandable why someone disclosing infidelity may want to do so anonymously; what matters is if the information/proof they provide sufficiently identifies the cheating spouse ... And it did. It doesn't actually matter who the CS cheated with it (or attempted to cheat with) .. and one can imagine there have been multiple women with this second FB account-having, long-term deceiver; what matters is the infidelity. No vague, improved allegations were made; clear examples and evidence was provided.
wanting to punish him regardless of who got hurt.
His wife would be hurt by the disclosure no matter what op's main motivation, and pretty much everyone agrees she had a right to know he was being unfaithful. So if she was to be told, she would be hurt.
The only way she wouldn't be hurt (by that incident of infidelity, at that time) would be if she was not told.
Op laid out her evidence clearly but did not say anything malicious, that I'm aware of, aimed at the cheater's wide. It wasn't going to be any "better" than that, while providing solid evidence.
You're being illogical.