I agree. At least 80% of your start-up depends on execution. You do need a good idea, but that's just the beginning and you can borrow heavily here (that's how progress works most of the time, improve on existing concepts). When someone 'steals' your idea and then does a terrible job at executing it, then I don't see a problem. You can just do better and prevail.

I have (supposedly) good ideas all the time, but not the time to execute most of them without totally loosing my focus. I'd actually be quite honored if someone would 'steal' some of them and execute them well as most of these ideas arise from some issue I encounter that needs fixing.