Well, everything has a positive and a negative side. YouTube has also some. Always try to take something positive. And the question comes how to take the positive side of something. Think about it. Realize it and then take a decision.
When you are trying to learn how to work with Photoshop. Obviously you tube can help you. On the other hand if you try to learn how to kill a man without being caught, that will be obviously harmful!
Hope you got your answer.