In logic there's a classic called a "False Dichotomy" - the example all parents know is, "Do you want to go to bed now, or in a half-hour?" The 'falseness' comes in that one is only considering two options instead of the multitude that actually exist.
If it IS a dirtbag/thug/badguy and he IS armed, then by all means one should defend oneself appropriately. Problem is , that's not the real world: you have everything from the ax murderer to the chihuahua next door coming towards you. (As a side note, I *did* have the neighborhood chihuahua aggressively approaching me and I was carrying... I chose to risk the bites rather than carry the nickname of "yap-yap" for the rest of my life.)
It might be best to train for and expect an armed assault from a determined aggressor - that way you have the ability and mindset to respond in a timely and appropriate manner. BUT... when the situation warrants a less than lethal response (think of the street photographer's thread recently) it would be very nice to have a proper tool. This would almost be a separate bit of training or drill, rather than a continuum of responses: in the real world, you are not likely to be in a position to do this:
"I'll try verbal, then spray, then draw, then warning shot, then clip him, then center-of-mass, then head shot..."
(OK, I'm over the top - but you get the idea.)
Instead, faced with a violent attack, it's
"If I'm in fear for my life / he has the Ability and Opportunity to kill me and has placed me in Jeopardy: I WILL respond instantly with lethal force."
So you're prepared for a lethal assault. But sometimes the assault (or jerk/drunk behavior) is fairly clearly NOT a lethal threat. I submit that one should prepare for that as well, AS A SEPARATE ISSUE,
"If I feel threatened by someone's actions but not in fear for my life (etc.), I'll have something other than hand-to-hand to deal with it."
And it is also useful to have the can of spray actually in one's hand while in the parking lot, while having pistol in hand with safety off may not be warranted. And a can of spray in hand with safety off COULD conceivably be used in the progression of force we would all probably like to be able to use: he approaches, I yell-spray-toss-the-can-and-draw... and if he has collapsed or is stumbling away then I reholster. But in this case the assumption and training is that Part 1 and 2 didn't work, Part 3 is in progress, and I'm willing and able to do Part 4 immediately if needed with little delay compared to a simple draw-and-fire.
And I am not keen on stepping into an unknown situation: imagine spraying an undercover cop: he's NOT likely to say, "sorry, old chap, wrong party" - rather, he's likely to draw, then I would respond to that threat... ugly, ugly, ugly. One of my church family and a guy with a ski-mask and AK? Easy - but that's not OC time.
I support Glockman10mm's concept, but am in the "preserve my family" camp: a bad guy is on his own. That said, avoiding the legal/financial hassles after a shooting is ALSO part of "preserve my family", but the emphasis is on protecting those God has given to my charge rather than protecting the bad guy from consequences to his actions.