Can A Man Grow A Long Mustache?
In some cultures it is still seen as a sign of arrogance (show of pride/dominance). In cultures where it is no longer seen as a sign of arrogance, then such a moustache can be kept. The point being that basis of this prohibition was arrogance, and due to cultural shift, if this arrogance is manifested in some other things now, then a Muslim should keep a check on those things instead of moustache. Additonally, moustache that covers upper lip also affects the dietary purity of things one eats and drinks. This should also be kept in check.