Clubs could be banned over racism
Again, I can't imagine what would happen if the NBA or NFL or MLB did something like this.
This the perfect example of a few bad apples ruining the crop. If these clubs are suspended from UEFA play, they lose money, they lose money they can't get the players who help them win and the spiral downward continues.
What can the clubs do? They have ushers, I assume, they have security for certain. They would escort the offenders out and flag the section the offenders were in (people tend to sit in similar places when they go to these type events).