Some companies pitching to Andreessen Horowitz et al. are a bit more than an "idea". None of them are likely to be labouring under the delusion that everything they say in that room is an absolute secret, but there's a big difference between some general idea of the direction of your growth filtering down to that VC's portfolio companies in the same space on the one hand, and on the other, a partner peppering you with questions about your business plan and then opting to found and fund their own "stealth" startup in that space instead...
It's absolutely a dick move, but as a founder you need to be better equipped than the VC to execute. If you can't make that case convincingly, you shouldn't be pitching.
