OP referring to BestChange Campaign IMO. So answers will be based on that.
But, a rule like if you post on some topics or boards then you will lose your slot, is it right approach?
No, but it doesn't mean CM have to pay you for spam on mega thread. They had warned their participants to avoid such as thread where likely no one will read your posts, that means no one notice their signature banner as well. So why they should keep a participant like this instead of find some quality posters?
The better rule should be, not counting those posts.
No, this wouldn't be a good solution. When 10% post are spam from your post history then its means there would be more. So managers have right to decide either you will stay on campaign or not. Not counting those post isn't a solution, because they like to pay a good contributor.
As per basic rights and freedom of speech, we all should be allowed to write anywhere of this forum (as long as this forum allows) and a campaign may exclude posts as per their rules from counting toward payment and should not cost the spot if minimum post count is reached after excluding posts which are done on excluded section/board/topics.
Strongly disagree! Who is preventing your freedom of speech? They aren't asking you to don't make post any board. But they told to avoid spam on Megathread and they consider megathread which have more than 5 page which is enough reasonable to me. Spam on mega thread means they aren't caring where they are posting instead of post read all the replies. They are just repeating the points already made. They don't like to pay such as participants. Why CM should follow our rules since they are the payer and we are the taker.
If you like your freedom of your speech then it's better avoid apply on signature campaign. You will found some users here that they aren't joining any campaigns even they are well reputed.
If you don't like the rules then follow below quote;
“If you don’t like a Rule…Just Follow it…Reach on the Top…And Change the Rule.” -Adolf Hitler