Man... Now that I think of it, I've been watching Let's Plays since video LPs first became popular in '07. Which is odd, since I'm not a member of Something Aweful, nor associate with many goons. Still, I like them, and I personally think its really great that people can use this formula as a way to share their enjoyment of their favorite games. And just think of this from a historic perspective; what better primary resource documentation can you have for media than this sort of real-time, immediate documentation?
I owe my username to Lateblt, who first perked my interest in the Quest for Glory series, and Let's Plays have been my best way to experience those games, seeing as I'm actually really terrible at Adventure games. (Screw you, Belegost)
While there are a lot of terrible LPs out there, especially on Youtube in particular, they're really great at gaining a whole new look on games you know, for expanding your understanding of games that you don't have the ability to play yourself or for being a source of endless amusement. I don't really see any reason to insist that they stop. And if all you're seeing these days is people who are just using it to subscription farm, maybe you should try looking harder, because there are so many great LPs out there by people who really love video games, and really give a damn about what they're doing.