Speaking of cancerous Let's Players, can we talk about the Yogscast? Because that's a malignant mass if I've ever seen one.
So first there was their Kickstarter,
Yogventures, back in 2012, where they raised close to $600,000 for... well, their own shitty version of Minecraft, basically. They raise the money, promise their backers a ton of rewards and bonuses, state the beta will be available by December of that year, and then... nothing happens. They don't even update for long stretches of time; there was actually a solid year between two updates. As it turns out, they gave the task of developing the game to just one guy, who turned out... well, this:
Remember, this is the result of two years and $567,665.
Now it turns out that he burned through all the money and can't afford to actually finish the game. Fans still haven't received a lot of the promised backer rewards either. Did I mention that several of those fans spent more than $10,000 for this?
They're also incredibly shifty when it comes to disclosing whether or not content on their channel has been sponsored (the most provided is usually a message that reads "Thanks to [company] for making this possible" slapped on the end of videos). To make things worse, they're now beginning a business model where some developers will pay them a percentage rate of the game's total sales over a vague period of time. What's to keep them unbiased in their coverage of the game? Not a thing. What if it's another person's content that drives sales for a game and not the Yogscast's videos? Sucks to be them!
It's not the end of the world, but it's pretty sketchy and sets a terrible precedent. Game "journalism" is bad enough as is, but I shudder to think of all the quotation marks I'd need if this promotional model ever took off.
TL;DR: Yogscast isn't killing gaming, but they sure aren't helping it.