The problem is that any ban should mean they will not provide any exchange services to you but should allow you to withdraw or at the very least send coins to an address they came from. That second option would suck for people who used coinbase address to withdraw from other services like online gambling sites but would be at least partially fair.
Stealing client funds is never the right way. I stopped using them a while ago after reading of people who had similar beefs with them.
If an account is banned you will never receive the funds and all of the services hold on to that funds until there is a scam accusation against them which forces them to do what is necessary and logical and we have seen that instance several times and there are situations when we provide all the documents necessary and it will take a long time to get our funds or the accounts unlocked. The only solution is to identify all these sites that have bad policies and avoid them altogether.