Yes, working in public does increase the chance someone will take your idea or get inspired by it. But generally I'd say that the originality of your idea is, or at least, should not be what makes or breaks your product.

I don't share everything I do publicly, but I do share a lot. I find that there's a lot of benefits (getting product feedback early on, expanding by network amongst makers, getting more useful advice, etc) outweigh potential disadvantages.