I don't even know what to reply to this argument other then what the dillydamn fuck.
First of all, not every lets play is based on just a playthrough of the game to show you how to beat said game. There is a difference between a WALKTHROUGH and a LETSPLAY. A lets play exists for the sole purpose of providing the user entertainment through banter and in game antics. If you've ever watched a RoosterTeeth let's play or Gamegrumps, this would be painfully obvious.
Second, You're argument about the soda is fucking stupid. You argue that seeing a person drinking a Pepsi isn't terrible advertising compared to a full LETSPLAY that shows the entire game. Guess what. You watched a person drink the Pepsi. Did you taste it? Did you get the EXPERIENCE of Pepsi from watching someone drink it? Absolutely not. Do you get the experience of a game just by watching someone play it? Hell no. Just because I watch someone playthrough Resident evil 4 doesn't make me not want to play it OR experience it for myself. It affirms my want of the game.
If you're so pissed off about let's plays ruining game experience, why aren't you shitting on Game Guides? I've been able to buy Physical Game Guides since the 80's, I don't see you shitting your pants over those either. Those "ruin the experience" and "make money off the content of the game don't they?"
And lastly the argument of "they shouldn't make money off this it's wrong." Is so goddamn stupid. They already bought the game so the game makers made money off said game. If anything, people watching them PLAY said game will convince them to want to BUY the game, resulting in MORE sales of the game.
I've never heard of someone not buying a game because "well I can just watch someone else play it." I guess back in the 80's when you sat next to your buddy on the couch and watched him play Mario, you just said "well I already watched him play it I guess I don't have to buy it now." Fuck that. You would run home to mom and say you wanted to get it too so you could both play it and experience it in your own way.
I've never heard someone so pissed off about let's plays before, it's the most asinine and bizzare thing I have EVER heard.