I've said enough on this, but yes, of course the people in there doing it have the most direct impact on performance
But 39,000 people in the stadium being supportive during difficult times vs 39,000 bringing negative energy is surely going to make a difference in terms of player and management psychology? So it is a factor
The fans just seem to think because they've paid their gate money, they have no other responsibility. Imagine if the owner thought that way - 'well, I've put in my £500m, I can take no responsibility and be massively critical of the team, management etc'
But of course, for anything to work, the owner needs to take a balanced view and put time and effort into trying to make things work. It's a shame some fans can't do the same and use their brains a bit more - I don't think a lot is expected of them - just a positive contribution when they are in the ground would be helpful I expect...