And I think he's right. You don't have to worry about somebody stealing your idea, as most people don't have the initiative, the drive and the tenacity to execute their own ideas let alone somebody else's. The poster is right, keeping your cards to your chest may do you more harm than good.
You tell somebody about your idea and they may either point out a problem with it that you need to solve, or they may become interested enough to become an ally or somehow involved. You may even realize that your idea isn't a good one, or that you're basic concept is flawed.
But in general, if the idea exists solely in your own mind, it runs the risk of staying there. Sharing it with others gets some reality testing and quite possibly some crucial refinement that makes it a game-changer.