^ Your grey area is your sense of responsibility, are you only responsible for direct consequences of your own actions, or does having knowledge of the consequences of other peoples iminent actions and the existance of an opportunity to intervein for the greater good carry with it the duty to take responsibility upon yourself?
If you are only responsible for what you DO then you might feel you acted against morals by shooting that one person, but if you consider yourself responsible for the decisions you make, encompassing that which you do AND do not do (it is still a consequence of your decision if not a consequence of your action. You should notice consequences can overlap, there is not one single variable responsible for any occurance, here the outcome is seen as both a consequence of the bad mans actions and a consequence of your decision, and there are countless others not mentioned overlaping, coinciding, all circumstances are consequences of what was before them, cause and effect), then you might feel you acted against morals by not shooting that one person. Basically what will happen is you will choose whichever outcome causes you personally the least distress (not the one which you believe to be morally right) and then you will create justifications and willful ignorance around the issue to convince yourself you DID act on what was morally right, therefore alieviating any guilt.
Either way you're still a moral person living according to their values in this situation, as it is decided upon completely out of need (protecting oneself from the greater trauma is a survival instinct = need), neither option is doing wrong for the motive of greed.
I've been in situations before where I have truely acted against my values, of course no-one is perfect right. It has been because of greed, I ate a meat pie once after I had developed the moral value that it is wrong and become vegan. It was because I didnt have this value as a strong conviction current in my mind, if I had put thought into it when I made the decision to buy the meat pie I would have made a different decision, but at the time I desired the taste and convienience infront of me and although I could have put thought into it and acted in accordance with my values, if I acted impulsively and distracted myself entirely, not concieving of the violence behind this product well then I got to have pie/ imediate gratification, it was a greedy pleasure impulsive act, certainly not a need. And while I ate it, I stopped myself from experiencing guilt by distracting myself with thoughts of justifications, it won't make a difference really, just this one time, i wont do it again, it's already been killed me not having it wont bring it back to life, etc...
So theres an example of why people act against their values, they are disconnected from their values at the time, and disconnected from others affected and therefore not experiencing empathy.
it might be relevant to add that I have recently been diagnosed with a psych disorder for which one of the criteria is an "unstable sense of self" so perhaps that was what caused me to be disconnected from my values, who i am, what i stand for, etc. perhaps other people have all sorts of issues going on that cause them to act against their values, or maybe some lie about holding a value they actually dont lol