There has to be a difference between "talking to everyone who will listen" and "broadcasting your idea to the world". You might want to talk about your idea to 99% of the people you meet, but specifically avoid 1% for one reason or another - putting it in front of an anonymous audience makes that control impossible.
I've yet to see that come true, ever. I've seen lots of people try to do that, but invariably types like that will go for the low hanging fruit. Their heart won't be in it and as soon as the next thing comes by that looks like less work they'll start chasing that.
Building a business takes dedication and tons of effort, the idea is a minor part of it all. Sure, you need an idea to get started but if your execution is excellent it will take a very determined party to try to compete with you.
