Well, a backdoor isn’t a problem if it is an client side encryption, with it they may access the cloud data but they will see only this, encrypted data, because not even the ckoud provider can desencrypt these data. If you are investigated, they must visit you in person with an court order to give them the locally stored or memorized encryption password or spend a lot of time and effort to crack the code, almost impossible depending the used encryption systemwith normally 256 bits or more. The backdoor only make sense if the Cloud provider stores an recovery code to restore your data when you lose ore forget your encryption password, which isn’t the case when they want to offer an safe and no knowledge service. In these loosing your encryption password is loosing your data, the price of security.