Facebook is an employer that has a legitimate reason to require that you have a Facebook account.

It never came up when I interviewed there :-) and I doubt it's why I didn't get the offer.

They were advertising products via facebook posts. They did check in on the account periodically to see if posts were being made.

Ah then it's normal, like an employee is supposed to participate in company's marketing efforts in that way. I see no problem with it, as long this is a part of the job and written in contract, i.e. something he's getting paid for.

It's not like they wanted me to make a Facebook account to keep tabs on my private life.

Cleaning toilets is also "normal," and you're free to see no problem with it. But if somebody acts like nobody has to clean toilets as a condition of emplyoment and calls anyone who says otherwise "disingenuous," I'm gonna call them out on being wrong.