I can see both sides of the argument - and I think when you see something like the "protein wars" that both sides are probably right and are getting different effects. I've heard reports of people gaining weight on high fat ketogenic diets, and losing weight as well.

High protein doesn't cause high blood sugar in most people, although I have heard of it in diabetes type 1 (Dr. Naiman mentioned it regarding type 1, not sure on type 2). I think most of the time people are eating a lot of protein foods that have fat too, and that will cause blood sugar to go up. Just eating in excess does it - the body doesn't have anywhere to put the extra fat that rides with the protein. He explained that in the interview on Ketogenic Girl's podcast/Youtube channel.

I have heard Ben Bikman talk about this effect as well - if I remember correctly, there are cases where it can happen but isn't a large effect (I can't remember if that was diabetes). He is the king of all things metabolic - I intend to dive into his lectures when I have time.