Since exchanges have begun blocking funds also on the basis of how “clean” they "think" bitcoins are or not, it has become increasingly dangerous to use centralized exchanges. They strive to make users afraid to withdraw funds to their wallets at all, so that later their coins will not be recognized as "dirty". They don't just want to get all our bitcoins and manage them themselves, they want to intimidate users into not wanting to get bitcoins outside of centralized exchanges (where it's not real bitcoins). Real bitcoins are only inside the bitcoin blockchain and nowhere else. And centralized exchanges are trying to gain control over real bitcoins with their division of bitcoins, but they still won’t succeed!