Where do we draw a line? Signature campaigns or shilling campaigns
That is a false dilemma.
As much as I understand his logic and I even respect him for stating that publicly rather than kicking out "misbehaving" participants without stating the reason - I think we have a precedent here where the campaign manager is openly policing (to a small degree but still) the content of the posts by telling participants what they can't post, or what they must include (i.e. you can't say you like product X without mentioning product Y).
This alone might not sound like a big deal, but the unwritten rule was that signature campaigns are nothing more than renting out advertisement space, and there was no expectation of participants to endorse advertised services.
That is simply untrue and what you call an unwritten rule is something you made up. It's much simpler than that:
➥ I reserve the right to change the rules and disqualify any post and any participant for any reason.
The signature campaigns operate under a free market regime. I don't know what supposed problem there is here, and I'm telling you that I was expelled from that same campaign for leaving a red tag to a Wasabi worker. You could also have applied that same argument and with more reason in my case. But the thing is as simple as that you are free to go to another campaign whenever you want and the manager can fire you if he sees that you do something that does not favor the company that has hired him to advertise.