FB allows commenting on ads. This does not go well for certain types of advertisers. Political and religious ads especially. Even the bland corporate advertisers have to spend some time cleaning up the inevitable mess.
What's especially puzzling is that FB allows image uploads as an ad response unless the advertiser was smart enough to disable it.
I am pretty sure I still get comments on my ads. It's almost entirely spam and those comments you think are probably spam it's just a 'good job' response.
Is that the case ? We (rsync.net) used to advertise on reddit quite a bit and we would have sponsored posts that had a proper comment thread and Q&A, etc. - I thought it was fantastic.
Reddit shadowbanned my account sitewide. That's enough reason for me to never, ever view Reddit without an adblock.