If you could only fire it three times, who'd be your Sun Cannon fodder? Skipping the three shot limitation, would it only be used on people who have personally offended you, or would scumbags you've never had to deal with be subjects? If the only limiting factor is your own sense of morality, what percentage of the population do you think would need to be shot into space for the betterment of the enlightened few?
Three times...I'd use them on real scum of the earth types. I would have to do research into who they would be, but I would choose 3 people who are still at large (under the guise of selling them the thing) with large human rights rap sheets. The Hitler's, Pol Pot's, and Slobodan Milošević's of the modern world.
I'd set guidelines in place for who could be fired. No one has personally wronged me to the degree that they should be killed, I'm not that sadistic, I just play one on the internet. I would probably draw the line at rapists, those who have tortured others, and some murderers - crimes where there was willful and wanton pain inflicted. People who can't be rehabilitated - and I don't think everyone can be, some people are just too broken to be fixed. "Crimes of Passion" would probably not be considered.
I'd guess maybe 10%, but they wouldn't be the kinds of people that would be missed. I joke about The Sun Cannon because I realize it's completely irrational. My honest opinion: There are lots of fucked up people, but most of them aren't naturally deviant, there is usually some external stimulus that causes someone to be detrimental to society. My parents weren't the brightest people in terms of schoolastic intelligence, but they understood living within means, budgeting, parenting, and being good social citizens. Results: Worst thing they, my sister, or I ever got was speeding tickets. They struggled to stay off welfare, but we weren't living it up. We lived in a one bedroom apartment until I was 12. That's four people sleeping in the same room for eight years because that's what they could afford. No cable TV or other nice luxories until my dad got a promotion and we were able to move out. They didn't resort to crime to get by. Unfortunately not everyone has my parents resolve, morals, and common sense. My mom wasn't spitting out children left and right. There were two of us and my dad worked two jobs so my mom could stay home and raise us without having to worry about going hungry. When I harp about dumb people, I don't mean people who are scholastically dumb, I'm talking about people who are socially dumb, like the guy who fathered 30 children to 11 different mothers and then asked the government for child support help because the only job he's qualified for is minimum wage (link:
https://wreg.com/2012/05/16/tn-man-fathers-30-kids-but-cant-support-any/). The mothers are part of the equation too. That's just one example. There are tons of examples of people who just don't get it. The rules of a functioning society are amazingly simple, but it seems fewer people seem to grasp them every year. I don't think I'm better than people because of my degrees, SAT scores, or IQ; it's the things that seem so simple that piss me off about other people. Things that were largely common sense, before everyone felt entitled to everything and were largely shielded from consequences. I'm not anti-social programs either. But the cycle of poverty can be broken, but right now it seems as if people aren't willing to make the sacrifices for themselves or their children to have brighter futures, and at the same time make decisions that outright harm others.
The #1 on your list is in your sights, the only problem is El Barto is currently cleaning the front of the sun cannon. You will never get another chance, it's either fire now or he stays on the planet unharmed, what do you?
I wouldn't trade an innocent life for one that isn't, period. Not firing.