A few points:
Agression has a definite place in most sports, particularly contact sports, it's just that it needs to be controlled as otherwise it becomes merely indiscipline, i.e. counter productive.
I would definitely consider boxing a sport, particularly amateur boxing since the focus is on point scoring (involving skill) as opposed to pro boxing where the ability to knock yer man's block off is an advantage (though skill obviously needed as well).
Damien Dempsey used to do a bit of boxing so I'd say it mighn't be fair to throw him in with absolute beginners (as I assume the others are).