Only pass kyc if your sure on the project where you pass your private documents. Fraud projects or programs that ask for kyc might use your info for illegal purposes.
No. They don't need your KYC. Why? Give me one good reason? Saying it is to prevent multi-accounting makes no sense because you trading your safety and everyone elses just to prove you don't have more then one account. There other ways of doing this and KYC exposure or leaking is 1000x more dangerous and damaging then any amount of multi-accounting can.