This thread is only missing a response from the all-knowing guru of defensive tactics... Leonidas.
I was just waiting for the "but take from them, EVERYTHING!!!!"
Although I agree that some criminals might have murderous intentions, I could easily look at the newspaper and assume every person in the country is a cop-killer. Oh wait, policemen are trained and armed, and they are still murdered every day.
Having lived in cities and been robbed once, I would never pull a gun on an attacker. Yes, there is the potential that they are of sound mind to kill/beat you so you don't remember them, but if they are smart enough (remember we are speaking of petty theives here) to remember that, then they should have been smart enough to wear a hoodie and a bandana (and as happened to me, he wore a bandana of the opposite gangs color). And then as such, they would then know that killing someone is much more an offense then robbing someone, and will draw more attention to themselves, and they will never be able to spend their money.
Now looking at the other side, a criminal without a clear plan, they a) probably don't plan on executing you, and b) are thinking of not getting caught doing it and bolting as soon as they get money. These types assume they can scare you, even with a water pistol. They take the stash and bolt. A purse snatcher is not going to stop to shoot you in the face... too much attention. They are desperate, and yes, no pleading will stop them and may even lead them to anger because you did the one thing they don't want, wasted time. So, give them your wallet, your watch, whatever. Don't delay them, because thats what they are trying to avoid at all costs.
The last bracket contains the psychopaths, and these bastards are going to kill/harm/rape you period. They desire to kill, and no amount of talk/giving/defense is going to stop them. None. You are going to die if you can't stop them. Even if you try to stop them they most likely have the jump on you and no amount of hand movements will convince them you are not reaching for a gun/knife/pepperspray.
So to me, if you have only 1/3 types of criminal looking to kill you outright because they are psychopaths, while the other 2/3 are only going to do it if you fuck up their (most likely ill-advised) plan, I don't see the point of not giving them ten dollars. If you meet that rare 1/3rd (and the percentages are most likely not scaled, only though type), you are going to die without being able to defend yourself or kick and scream if you wanted to in the first place.
Most muggings/robbings don't happen like they seem to in the movies, with some gangster coming up on you with a loaded glock and demanding your money or in an alley in public (why the hell would you be in an alley). Instead it happens exceedingly subtle. Person walking towards you or behind you. Gets in your way, and says only: Give me your wallet. Your immediate disbelief quickly turns into fear as you realize you are getting robbed, and this guy (if you are not paying attention to your surroundings or look like a loaded target, which is what they look for) has come out of nowhere (to you). I didn't care if I saw a knife or a gun, I opened the wallet, and gave him my cash. And then he was gone around the next corner. I got back safe to my Dorm, shaken up to hell, and called the police. Gave them the description, said they doubted if they could catch him, and that gangs wear rivals colors to get away easier. They caught the dude later, but not on the same charges unfortunately, through a snitch.
In my honest opinion, being abrasive in something as petty as this leads to more people getting killed over something as insubstantial as money than those who give and let go. I in no way believe that the "making them feel guilty and talking them out of it" works in such a quick scenario, and of course to the rare 1/3, it will likely accelerate it.
If my family were on the line and not money I can make back (unlike those scumbags), there would be a different story. Its not black and white unfortunately, so even what I say here could change in a heartbeat when something hits the fan, but taking a pure abrasive stance is just as bad as trying to "talk" them out of it.