Yes, if you try to disarm a knife-wielding dude you'll probably get cut. Probably get cut pretty badly. What of it? Would you rather he kept his knife so that he can keep stabbing and slashing at you indefinitely?
Look, I'm really not sure what you're on about. I think you're reading things into this discussion that aren't there. Nobody said knives were useless, or that you shouldn't carry one, or that you shouldn't use a gun, or whatever else you seem to be imagining.
And you also seem to have some rather romantic notions about knife fighting banging about in your head, about it being an easy and clean and pleasant business. I think you might be wise to work those ideas through, just in case you ever need to fight with a knife or against a guy with a knife. You don't need to be an expert, and I'm certainly not an expert myself, but a little perspective might go a long way.
Now, please, can we get back to the regularly scheduled SHTF-guide-for-noobs thread?