I'm disinclined to judge people too harshly for that. Self-interest, like all other aspects of life, isn't objectionable unless it meaningfully interferes with the ability of others to live their lives. Someone who is entirely oriented around personal survival? Okay, yeah, it's selfish, but I'm not going to condemn them for a natural response to a terrifying eventuality. If they cross that line and start harming others for the sake of their own survival, then it's an ethical issue. Someone who runs away from an armed gunman when there are other, more vulnerable people present isn't admirable, but they're not the same as someone who pushes those other people into the line of fire to help themselves survive.
Funnily enough, my personal ethics almost flip what you are saying on it's head. IMO the rules in descending order go:
1) Take steps to give yourself the best chance of survival.
2) Take steps to allow as many other people as you can to survive, possibly at the expense of others (but not yourself).
So if it comes down to just me or you, then I'm not sorry, but I'll be pushing you in front of the gun, and from my ethical point of view not only will I be justified, but you will be justified in fighting as hard as you can to push me in front of the gun. Under my system fighting for your life, even at the expense of others, is always ethically justified, but them fighting at your expense (potentially causing conflict) is also justified.
That said it's important to note that the most likely to lead to me surviving in the short term is not necessarily the thing that is more likely to lead to me surviving in the long term. Throwing you at the gunman might be an almost guaranteed plow to buy me a few more seconds, but working together with you to take the gunman down, while less likely to buy me those few more seconds, is much more likely to buy me the rest of my life. Aiding others works the same sort of way. Being nice to people doesn't really cost me any of my current lifespan (in the vast majority of cases) but could lead to vast potential increases in the future. (Unlikely to, but somebody has got to win he lottery eventually, and unlike the lottery this doesn't actually cost me anything other than stuff I'm already paying).
The way I think about it is like this; if everyone is selfishly guarding their own life, even at the expense of others, then they will be taking the maximum steps to protect themselves from potential threats by eliminating them. This has the side effect that for me, being selfish, it is in my best interest not to become a potential threat to other people unless absolutely necessary; i.e. if we band together to kill all of the murderers as potential threats, then it is in my absolute best interest not to be labeled as a potential threat. Balanced against the aspect of ensuring your own survival, this means that even totally selfish survival people will still work together unless there are no other options.
Strangely enough this can also lead to cases where from my point of view, ethically, both the villain and the hero of a story are "in the right". If the villain is trying to save millions by killing thousands, then they fall under rule number 2, which says that they should save as many people as possible. On the other hand, ethically, rule number 1 says that each person in those thousands should fight as hard against the villain as they possibly can to ensure that they don't die. It can make for some very interesting stories where, for me at least, who is the villain and who is the hero can almost flip-flop depending on whose point of view the reader is currently watching through.