People criticize the idea of "rationalizing". They will say that humans can rationalize anything. If I am on a diet, I can find a reason for eating a piece of cake anyway ("It's such-and-such's birthday, I have to celebrate!", etc.).
The problem I have with this is that rationalizing is not bad. Anytime we are faced with a dilemma, we have an emotional reaction and an ethical intuition, then we seek to rationalize that response. This is much, much better than to NOT seek to rationalize our response!
Of course we rationalize - as if it were possible to have a completely neutral, unfeeling lack-of-response to an occurrence, and then to do some rational calculations and act on them. We would all live in a state of paralysis. We have to act according to our intuitions all the time.
So the question is not "Should I rationalize?". The question is "Is my rationalization successful?" If it is, then great! If not, then perhaps some personal exploration may reveal something that needs attention in ourselves.
But how do we judge our rationalization? By more rationalization and intuition (like the ones we first started to rationalize!) So really we must weigh our different ethical intuitions against each other using our reason, and decide what the best choices are.
In other words, I guess we do our best!