There are lots of benefits to talking to people about your idea. You’ll get suggestions for improvements. You’ll discover flaws and hopefully correct them. You’ll learn a lot more about the sector/industry. You’ll learn about competitive products that exist or are being built. You’ll gauge people’s excitement level for the product and for various features. You’ll refine your sales and investor pitch. You might even discover your idea is a bad idea and save yourself years of hitting your head against the wall. In terms of the risk of someone stealing your idea, there are at best a handful of people in the world who might actually drop everything and copy your idea.