It's an interesting reaction in here to Ben Foster's comments. A mixture of telling him where to go or that the players should respond to criticism in a different way.
Ben Foster wasn't saying that the fans are the reason that the club are under performing over years But he has pointed out (from any other ground or team he plays against) that the fans can be a factor. Here he's used it as a negative, or at least provided a negative example. Which it undoubtedly is at times. It can also be a positive when the opposite is true.
Everton's issues aren't down to the fans being negative. But it's contributory factor. How small or big? No-one knows. I'd suggest it's relatively small.
The important piece you need to ask yourself though, as a fan, is how you can influence what happens on the pitch. There's off the pitch stuff that any supporter can do, in a positive or negative manner. But the main interaction between players, manager, club and fans is at the game. You have an opposition player saying that his team (and likely others) know that you can use Everton fan's reaction against their own team.
If that doesn't get you thinking about how your actions at the match can influence things, even in the smallest manner, then nothing will. It should provide some self awareness and reflection from parts of the fanbase rather than completely dismissing it.