The following are my opinions only but are predicated on 26 years of dealing with criminals as my job and on extensive firearm training ("tactical/combat", self-defense and otherwise) during the same period of time:
(1) It is always a mistake to try to "catagorize" an offender. Criminals can be smart or stupid and everything in-between. Those of you who think there's no difference between a drug-crazed individual and a sober one in terms of possessing a rational thought process (everything else being "equal") simply haven't dealt with enough of them. It doesn't take rational thought to rob someone and it requires irrational thought to resist arrest when faced with overwhelming odds.
(2) Never count on the mere display of a firearm to scare off a determined criminal. Yes, it might happen but do not count on it. Anytime you brandish a weapon against another person it had better be for a legitimate reason (in most states that means you have good reason to fear for the loss of your life or limb or that of an innocent other). And if you have a legitimate reason for pulling a gun on someone you must be prepared to kill him.
(3) Killing a person might not stop a criminal from slaying or maiming you (doesn't do you much good if he later expires in a hospital after leaving you dead at the scene) and stopping a bg from committing his crime may not require killing him. This seeming paradox is the reason it is important to bring a man-stopping caliber/cartridge to the fray if at all practical when your very life is at stake. Many-and I am one-believe that the minimum requirement needed to reliably stop a man in his tracks or to keep him from taking very many steps is a .357 Magnum "and up". This isn't to say that a lesser caliber should not be considered. Climate, social circumstance and other factors may dictate toting a .380/.32 ACP or some such as opposed to having nothing but a set of keys to defend yourself with.
(4) Finally, don't kid yourself. Having more ammo than needed is a far better scenario than not having enough. Simply being a good shot or having completed a firearm self-defense course is no guarantee that you won't expend more ammunition than is "needed" on a single individual during the heat of the battle when your adrenaline has reached a peak you have never experienced before or that you won't be faced with multiple assailants. Many seasoned, well-trained and cool-thinking cops have fired many more shots during a gunfight than "necessary" due to their elevated stress levels, poorly-lit environment, moving "target(s)", etc. It is worth remembering that no one has ever complained about having too many bullets on board during a gunfight. The reverse is not true.
All that said, I believe a Ruger LCP (or its ilk) has a definite place in one's ccw "wardrobe".