Unfortunately lead Bitcoin developer Gavin only left us with this level of peace of mind on the 51% risk: (paraphrase): "Bitcoin is still a young technology. Only invest what you're willing to lose".
well he is not going to say throw everything you got at it. even smart gold hoardrs wont tell you to throw every penny at gold. the only people that would say throw it all in, are th people that want your money so they can cash out, because they are greedy and selfish.
i have yet to see a honest life insurance guy say, put all your salary (after bills) into life policies
i have yet to see a honest stock trader guy say, put all your salary (after bills) into life policies
i have yet to see a honest forex trader guy say, put all your salary (after bills) into life policies
i personally think bitcoin is robust and has a long life-time ahead of it, and huge potential for profit, but id never tell anyone to throw everything at it.
anyone telling you to throw it all into an investment are usually the ones that know something is gonna crash and they want you to be left holding their old bag of crap. (EG pump and dump altcoin devs)