One of the reasons for making KYC mandatory is to prevent money laundering. Every country has a law and when a CEX does business globally it can do business in those countries as per the laws of those countries and that's why KYC is being made mandatory gradually. Binance made kyc mandatory long ago. A few days ago Kucoin made kyc mandatory. Still exchanges like MEXC, Gate.io allow trade, deposit, withdraw without kyc but very less amount. In future they may also make kyc mandatory. So it is better to complete kyc beforehand
Asking KYC to prevent money laundering is pointless, what if the money launderer use stolen KYC and successfully laundering the money? what will the centralized exchange do? if they report it to SEC and it mean the SEC will accuse a wrong person since the hacker is using stolen KYC.
Nah, it's worse to complete KYC beforehand, the best is just choose a no KYC P2P or decentralized exchange.