Many of the best posters wear a campaign signature as a means of passive income or play crypto, and the fact that they bear a signature does not cripple nor interfere with their ability to post.
I believe that good posters are just serious people in real life.
Wearing a signature that pays in BTC is an incentive to make even better posts, and spend more time in the forum (an in cryptocurrency subjects in general).
As wearing a signature these people can earn extra income, it is a nice incentive to keep posting, studying and helping new bitcoin users around the world. You are also helping serious projects, such as gambling, mixers, and other bitcoin related services. And you are also helping bitcointalk.org website, by contributing with good posts and helping users. I really see no problem.
Problems appears when managers are accepting spammers to their campaigns. Users that do not contribute to anything and are like parasites (as the managers who accepts them). Luckily, most of BTC paying campaigns are not managed by those people, and those spammers are mostly in altcoin related projects.