I don't ever give KYC for airdrops. There is no proceedings. I am not their customer or client. Why would they need to check my income and source of funds? It makes no sense at all.
Well KYC doesn't necessarily means they'd have access to your income or source of money. Anyway your personal details are however at stake because you submit to unknown people or company. Also, it depends on the type of project, some projects will actually require every holder to go through KYC.