Even if all they care for is only exposure, this still doesn't mean that they are deliberately encouraging spammers. I think that any service would prefer good posters to spammy ones. There may be just not enough good posters currently looking for participation or the payment is too low that only compulsive spammers get attracted by such a campaign.
No, this does not hold true. There are some services, which have been contacted several times by staff members in regards to the problematic spam generated by their participants. Those services have completely ignored these messages. In addition to that, there are some that use bots to manage their campaigns which is horrible
This had to be expected. How can they be held responsible for some users posting shit? Did they enroll these users themselves? No, they didn't. It is a campaign manager who accepted such posters, and he is in most cases not affiliated with the service. He typically has free choice in selecting users for the signature campaign he is going to manage, though...
Apparently, you are hitting the wrong target here (and missing the right one)
Therefore, the campaign managers are the ones who should be dealt with and where it will be most effective
Disagree. It's going to cause a even more complex environment with likely the same amount of spam.
Why so? If a few indolent managers get banned eventually, the wannabe ones will be more careful and particular in both picking up the job of a signature campaign manager and accepting new participants into the campaign