I wasn't aware genealogy was private. I'd assume the opposite, as birth and marriage records are public matters. If I were to post a public tree and someone berated me for it, I'd be dumbfounded at their reaction.
And you are totally in the right.
It is if a large part of your family is poor or you're related to a felon or political extremist. Sure it's not as private as bank records but it's not the kind of thing anyone with a brain would want to make it trivial to find.
Security questions by default often include Mother's Maiden name.
There has never been a point in the past 20 years when someone's maiden name was difficult to find.
Indeed, I sent an e-mail to my family when I published the genealogical information online. She sent me her concerns years later. It seems she haven't paid attention to my e-mail.
I had the exact opposite and had to call a relative, in her 70's, to remove me and my bit of the family from her genealogic tree online.
I'm actually surprised that you would break someone else's privacy like that.