I agree with MP, noblock actually makes knifing easier, and hence, I am all for it.
The biggest problem for knifers is running into someone with full health head on who has an automatic. Sure you get the first slice off, but then they blow your head off with their automachineshotty. With no block, you basically knife them head-on, run thru them before they can react and then knife them from behind, thus leaving them butthurt and bawwing.