Many people say that online wallets aren't trustful and that it's easy to steal your BTCs from there. No safe and guarantees.
I would like to know if you already had any problems with this kind of wallet, specially, Blockchain.info. Were you hacked or anything like that?
You need to distinguish some things first:
1. Are you worried about security of the wallet itself? Do you think that it is easy for hackers to break and transfer peopole's BTC from online wallet?
2. Or are you worried that actual wallet owners can rob you and get away with bitcoins?
3. Lastly, your account can be hacked individually.
About Blockchain.info - I never heard anything bad about this wallet. There wasn't any known hack documented, ever.
Also they won't close or suspend your account because you send money to gambling service or something ridiculous like their competition.
With blockchain the weakest link is owner - only if hacker will know your password and wallet id they can steal your coins.
I feel that with 2FA enabled it is almost impossible though.