Can you tell which campaign is doing this ? I have not seen any signature campaign doing this so far from different campaign mangers in signature campaigns which are paying in bitcoins. It sounds really surpassing because there is actually no need of email for payment.
The OP is not only talking about the signature campaign, He is referring about the bounty campaigns like social media, translations, etc. Which is, those bounties are not paying BTC they only pay after ICO with their tokens.
There is an issue with bounty managers, they are just exposing participants email ids. In my opinion, it is not a right thing at all, it's just unacceptable.
I don't see negativity effect with that its only my email and I think its more helpful to be updated on the project we are focusing on. My own concern of joining a bounty is providing us KYC for a deal just to receive the payments and its not worth it. I think that is one should be change.