While that's possible I would say that's extremely unlikely, so you're better off getting the feedback.

Think of this way, on the spectrum of loathing to loving your idea, they have to be on the top end and have either the resources or technical knowledge to execute, and now they have to pass you who has a hypothesis already and is looking for feedback. They don't know how much or what you've already gotten, so if they flat copy/paste based on what you've spoken to them about they could be heading off in a different direction. If that's the case they're not really competing with you because they're somewhere else in a different niche.

One of the best ways to protect yourself from patents is to have the idea first and publish it. It's hard for a patent applicant to argue the he is the first inventor and that the idea was non-obvious if it was published in a blog.

corporations care about ideas being stolen because hundreds of millions are at stake. When you are a startup you have nothing to lose and everything to gain. that includes telling everyone about what you are doing.