This wasn’t some “good hit” cheering. Any fan is justified in giving an immediate cheer when an opponent goes down. Most of the time the injured player is able to get back up, or at least move. When they don’t, any self-respecting fan knows to be quiet and considerate.
Irvin was down for a long time, not moving at all. If you were watching, you know the fans (many; I won’t say all) were being disgusting. Do you remember the resounding cheer that went up when the ambulance came on the field? When they immobilized Irvin’s neck and put him on the stretcher? I think that would fit your definition of morally bankrupt.