You don't understand what I am saying. A loud stadium with noisy fans is a morale boost to the home team but mainly has a negative effect on the visiting team.I feel like you still don't get what I'm saying.
We know that a full stadium with noisy fans should boost the home teams performance through increased morale.
Old Trafford, while quieter for some years, still has a mostly positive effect by the mere presence of 76,000 or so people.
Without those people, though, a very large ground will have a greater inverse effect than a smaller ground will.
Where would you feel more intimidated as an away player?
In a 40.000 capacity stadium where almost everybody is making a noise singing booing standing etc
In a 76.000 capacity stadium where its mostly quiet, everybody is sitting down and has the atmosphere of a theatre.