originality and friction
Ideas are amazingly overvalued in the startup world.
Even in precise and theoretical disciplines (e.g. math, physics), a tremendous amount of propaganda is required to get an original idea accepted. Some of the greatest ideas get pushed into the fringes and stay there for decades, either to be rediscovered later by someone with more social capital or to be entirely erased from the collective memory.
In the imprecise and pragmatic world of startups, it should be even tougher for an original idea to propagate since there are additional executional hurdles on top of the already existing social frictions. (If an entrepreneur encounters only executional hurdles, then he should question the originality of his ideas.)
Hence there is no need to panic about a truly original startup idea to be stolen etc.