To be fair, the Boss is a violent sociopath. Ever taken the sidewalk instead of road in your car because it's funnier? Ever gone and shot a number of peds in the head for a couple bucks? Or maybe used the giant foam hand to club them halfway across the map for laughs?
Imagine that in real life.
THAT is why Julius tried to stop you. You were obviously a real problem, he unleashed a monster. Of course, the Boss is YOUR sociopath, so you take offense to that. It doesn't change much, and heck, it's not until the fourth game that the Boss mellows out and starts to be apologetic for stuff. I laughed at Kinsey's "Surprise! I was always an asshole!" line because it's so true. Sure the Boss is loyal to a fault and will happily escalate to brutal torture and murder to get back on, well, torture and murder.. but that doesn';t mean the Boss is a nice person.
It does make for a wonderful thing though. Volition gives you freedom to be as horrible as you can, and then calls the player out on the stuff they end up doing. It's rather brutal, and you do end up playing a violent sociopath unless you REALLY try not to, and even then it's hard not to when missions and activities call for it.