Insuring their hot wallet might let Coinbase increase its size, but it offers no extra protection for consumers. None whatsoever.
Also, I feel safer using a business that can't lose 3% of its assets in seconds, no matter if it would be stable either way. I'm surprised that you don't. (And yes, safety is the same thing as protection.)
However, I still think it's really odd to only insure the hot wallet and to call so much attention to the fact that it's insured. Imagine if your bank called attention to the fact that they were insured with large, high-rated insurers for any conceivable loss... and then they mention at the end that the insurance only covers what's in the tellers' drawers, not what's in the vault. Personally I'd run far, far away if I saw something like that.
It's bad that they have no insurance on the cold storage, but that's something you can't really get anywhere as far as I know. I take it more as a risk of bitcoin in general.