It depends. Given that a majority of Let's Play uploaders like talking about how average their lunch was, the experience is distorted by other player's experience. It'd be same with movies.
For example, Dreamfall is the type of game you can either play or watch since a player basically runs from one cutscene to another with minor exceptions.
Indeed it depends. Some games are cutscene heavy, they are basically movies. I can see an issue with those. Others, I think most, say Borderlands for instance, must be really boring to simply watch. A tycoon game where you see someone else take decissions could only be interesting to learn from those decisions. And what fun is an RPG where you don't get to choose how the character acts? Or a platformer where you see a guy flawlessly complete a level, I just don't see the point of watching that.
I think that when people say "LP is more about the guy playing than the game itself" they mean that if they simply put the game out, it would be so boring nobody would watch. The fun in watching has to be on their skillfull commentary, and I'd say that if this is indeed their selling point, they should have the chance to get money out of it like any other entertainment. Because they are the ones drawing views to the adds. And this isn't the case, why not have a publisher upload a video of a playthrough of their game, monetize it and take down everything else? It would be the same, would it not?
This all said, I still don't see a point in let's plays. I've never seen one, and I have zero interest in ever watching one. But while I can understand publishers of movie-like games being against LPs, and I don't have any respect for people who would upload a movie-like game effortlessly and get money out of it, I see no reason to block the kind of people who can make interesting entertainment from an originally boring footage. Even if that entertainment is not for me.
And sure, nobody stops anyone (yet) from doing it as long as they don't get paid for it, but if they do get paid and have their full time to dedicate into it, it stands to reason that there will be more content of higher quality. And quality entertainment with variety is always good by my book.