In order to be able to decrypt your wallet you need your password. And password is not stored on blockchain.info's servers.
So blockchain has no direct access to your private keys, they would need to hack your password first.
Also there is second option to manage your private keys while using Blockchain.info it is called Zero-Trust Mode - you add only your Bitcoin addresses without private keys.
I have said it many times but it is time to say it again and again until people learn that any online wallet should not be trusted. You are relying on third party to manage your bitcoins for you which is not the wisest thing to do when dealing with bitcoin. You can try a desktop wallet like electrum and multibit, both newbie friendly if the users have used online wallets before. Ultimately if you can afford go for a hardware wallet and keep your bitcoins safe for eternity.