Humor tends to be pretty subjective. Upon watching the movie, we laughed a number of times. While it certainly isn't the intellectual's cinema, it's got some dark humor that made us laugh more than once. Maybe it just isn't your flavor?

1. Georgia was there for the bounty, same as the rest. She came prepared with a gun, mind you, so I'm sure she knew that she was putting herself in a potentially dangerous situation. While she absolutely got more than she expected, visual storytelling shows us that she was a badass chick who was ready to get her hands dirty to get her payday.
2. Sharice went on her rampage as an emotional reaction to seeing (she thinks) the corpse of her partner, who she seemed to be holding a candle for. Again, visual storytelling is strongly suggesting to the viewer that she's very upset and not thinking rationally. If she had been thinking things through, she should have instantly packed up her hardware and split, realizing that things were getting too heavy. Regardless of who she was shooting at, it just didn't make any sense. Emotional reactions tend to go that way.
3. Again, visual storytelling comes into play here. While it's been a few years since I've seen the movie, you can see that Richard is very upset at that point in the story, having been through hell and lost a great deal because of the whole situation. If you'll recall, it is revealed that Buddy Aces and his father were both being protected by the government, despite all their heinous crimes. Everything that he had gone through that day - including seeing his longtime friend and partner murdered - was done for the sake of protecting the life of a truly evil criminal, who was created by the government ! The whole situation never would have existed, had his own people not caused it, in the first place; but it did exist, and it was an absolute shit show. What's even worse than that, is the fact that Andy Garcia just didn't seem to care all that much about the lives lost, or the impact the whole thing had on anybody, as long as he could get info out of Primo - info which may or may not even exist, but Garcia thinks probably does. It's just such a stupid situation, when you boil it down, and you can see that Richard is just broken at the end of it. He seems to just give up and decide to unplug Primo and Buddy, to fuck over Andy Garcia as a means of fucking over the whole bureau in return for what they've done. It takes some suspension of disbelief in order to buy that he'd make that choice, but that's what you get in Hollywood.
4. Whether or not anybody can survive and for how long after having been taken off of life support, would naturally come down to the individual involved, their illness, their fortitude, etc. It is very firmly established in the film that Primo is in dire condition and hanging on by a thread. Buddy isn't doing much better (likely an overdose) and they're only keeping him alive so they can take whatever pieces of him they need in order to save Primo long enough to pump him for info on the mob. As far as the government is concerned, they may or may not even keep him alive after they have what they need.

I think the movie probably takes a very specific taste in order to enjoy. I've seen it maybe 3 times, and not recently. Don't have any urge to see it again any time soon.