It's worth noting that this is exactly, word-for-word, how I wound up losing money in the Mt. Gox collapse. I was lazy. I liked their two-factor authentication. It felt safe, and I liked that no thief could steal my coins without access to my phone. I simply didn't stop to think: what if Mt. Gox failed tomorrow? And then it did.

The problem with Bitcoin right now is that it isn't convenient, even if you use these third party services. It's not convenient having to trust the services to provide you with convenience because if they fail, you fail.

But, ultimately, if you don't mind losing your money, it doesn't matter whether you trust Coinbase.

That's an argument for why you're willing to use it, but not for why anyone should trust it. If you're lazy, it's easier to not have locks on your doors, but that's not secure.

Use Electrum for the bulk of your funds and Coinbase or another provider for the ease of use. Don't store all your money with a third party.