At the very least, with a good campaign manager like yahoo the sig campaign participants are on a leash & the worst shitposters are not allowed in his campaigns.
I do agree with this, but there are other things to consider here.
When yahoo62278 initially took the job, it was to advertise CryptoTalk, not YoBit. There was a general consensus that if they were going to spam the hell out of the forum, then there should at least be some sort of oversight, as you state, and I pretty much agreed with that. CryptoTalk, although a cesspit of spamming, isn't a scam and no one has ever lost money on it. At some point along the line, two things have changed.
Firstly, the advertising is no longer for CryptoTalk, but for YoBit. YoBit's InvestBox (their initial signature) is 100% a scam, and no one can seriously argue otherwise. Because of the uproar surrounding this, they changed from InvestBox to an AirDrop signature. Marginally less worse, sure, but I still have major issues with users promoting a company which makes products and services designed to steal from other users, even if they are not promoting those exact products. As a random example, if people started advertising a Bitconnect lending service but said "It's OK, I'm not advertising the Bitconnect coin", I suspect negative ratings would be pretty quickly forthcoming.
Secondly, at some point yahoo62278 transitioned from simply having a role banning the worst of the spammers, to wearing the signature himself and apparently enrolled in the campaign, which as pointed out by nullius, lends an air of legitimacy due to his (yahoo's) trusted and respected status to what is an otherwise very shady/borderline scam campaign.
As also pointed out in other threads about this, however, the majority of altcoin signature campaigns fall in to pretty much the same category. Much like the coins on YoBit's InvestBox, the vast majority of altcoins are entirely fake, designed only to make the owners money and are then never heard from again.
I think given the first point I have made above, the correct course of action now for individuals is to leave the campaign and remove the signatures, but given that the campaign is due to finish in two days' time, then that decision is going to made for them.