I have been wondering of people telling me exchanges can freeze accounts, that makes me very afraid to use exchanges to trade,  a friend of mine told me hitbtc freezed his account. That makes me here to ask the reason why exchanges can freeze account.

Why are exchanges freezing accounts?
What can I do to make them not freeze my account?
What are the best exchanges to use?

I like no kyc exchanges, please do not advice me to use any kyc exchange. I prefer exchanges that do not demand for kyc or the ones that makes kyc not mandatory?