In this particular case the woman is doing of her own free will what she wants to do. There is also nothing wrong with someone voicing a concern about it in a private message.
Absolutely. Even interviewing people who do sex work, when you claim to be a CSA advocate, is really "off" and if he wasn't such a pompous ass he'd appreciate the valuable feedback someone was giving him privately. To then make it public so he can play little miss victim about it, very bad etiquette.
And if being associated with sex workers through interviewing them raises concerns for how it looks to someone professing to be an advocate is bad, that means he can't be surprised that going off to regularly use prostitutes for many years, some half his age is thoroughly incompatible.