I honestly think they are.
You have to think about this, when people don't what to play a game correctly I.E. cheat, glitch, or hack. They google it, and 9 times out of 10 they find various youtube videos about it. After they watch it, they go and exploit it to the fullest.
I will admit that I did glitch GTA Online when I was on PS3 because getting money is ridiculously hard at low levels unless you have someone running RTR for you.
But R* did punish people for doing it by either resetting them, banning them, or taking all there money. But the punishment isn't the same for youtubers. Yes they can be reset or even banned, but they have the ability to go out and wither start a new Account or buy a new xbox etc which many have said they've had to do (in a very "better then you" tone of voice). Normal gamers dont have that ability. (If you do, good for you).
Another glitch that has become popular as fuck in BF4 is on the map Operation Locker. Most you who play BF4 know what I'm talking about. In the center part on the map (Conquest) there is the central prison area. You are able to glitch into the prison walkways surrounding the whole objective. Only a few people knew about it for a while, but once youtubers made videos about how to do it, you are now guaranteed to have it happen in every single game. Why? Because people will always look to get an advantage weather it be legit, or glitching in the case. That's just how people are wired.
So I ask you, do you think Youtubers are starting to ruin games?
My answer is yes.