I never said you get the full experience. I said that one can experience the best parts (which matter to them) of certain games that they intended to buy without buying them and then they can change their opinion about buyign the game. It wasn't like the cutscene was free to make, yet somebody still gets to experience said cutscene free of charge. I experienced the parts of Halo 4 that I wanted to experience - the story, and I didn't have to buy the game. That in my opinion, is partial IP damage on the part of the content distributor (I don't consider piracy theft I consider it property damage, for example.) I don't think people should complain when they can't get away with it.
To each their own on that. I believe that if someone sees huge portions or mere minutes of game then it's like advertising. Doesn't mean that everyone who sees it will want to buy the game but it does help sales some. If the game is good then those vids should really help sales. Advertisers get paid though. Youtubers are basically the same thing and should be able to make money off of advertising a company's product. Consumers shouldn't pay money to see those advertisments.
Not all advertisement is good though. A lot of developers don't provide demos, for example, because demos can hurt game sales just as much as they can help them. If one's opinion of a game is dependent on the let's player and not the actually quality of the game or Nintendo's personalized advertisement, then there can be unforeseen negative consequences and risks just as much as there can be positive ones. Here's an interesting Extra Credits video about the topic of demos, and I think they can be applied to let's plays as well.
