I can't honestly see why any developer would have an issue with Let's Plays.
Well, especially with point/click adventure games, even if there is branching, you can easily turn the game into a "watch your own adventure" thing. There are other games that have relatively weak gameplay with a strong story that can easily suffer from a let's play. Games that exist "as a work of art" suffer, even if they have okay gameplay, since they're more visually driven than player interaction driven.
Also, do remember, Google has decided (with questionable legality) to pay people for uploading "popular" content. The instant someone profits from the upload of a video containing any copyrighted material (such as let's plays) it becomes much easier to show that fair-use is not a valid defense.
Let's Plays of horror/jumpscare games has been somewhat of a driving force behind the sales of a lot of these games, even though I have never seen the point since they spoil what scary thing happens when. Also the feigned-girly-scream men give me a headache.
I'm not sure how strongly that is the case for 'interactive story, aka walking simulator' games. I recall The Stanley Parable faring reasonably well mostly from word-of-mouth advertisement, but haven't really played any linear, interactive stories.
Youtube videos do make money, quite a lot even for some people. This has obviously led to some shady practices like 'reaction videos' where a whole episode of some show (or other youtuber) is played from start to finish with someone making stupid faces next to it. The reaction video maker gets all the ad money, and viewers are not going to be too tempted to see the original because they already saw the whole thing.
But games are kind of a different beast. They are interactive and seeing someone play a game can be a lot like that time you were a kid seeing another kid playing with a cool toy. It suddenly makes you want one of those for yourself to play with. Sure, there will be people who watch the Lets Plays but do not buy the game, but those people likely would not have bought the game at all. They still cost you no money, and for each of them there will be some who might try the game even though they would not have considered it otherwise. I know for instance that a lot of DF players picked up the game from reading/watching Lets Plays.
I feel that all got a bit rambley...
Anyway, I will amend that first quote to 'Unless your game has little interaction and branching storylines, Lets Plays will be a net win for you as developer and might even replace traditional advertisement.'