I think it is important to express emotion. This trait and our ability to rationalize it separates humanity from most animals. However, I do not support being a whiny little emo-kid, who cries when something unimportant takes place. Emotion is a powerful thing, and it would underplay its power for me to say that you shouldn't cry when you see something distressing, be it soldiers on the news, or that one scene from James Cameron's Avatar where the big tree falls over.
I think crying is wrong if you are crying about something that only effects you. You are just wasting energy that could otherwise be used fixing your problem, instead of making yourself feel worse.
Yes I think men can cry. Should they cry as often as women? Absolutely not. Men have taken a beating in the gender war recently, and while I agree with equality, I don't think that means we should start acting like girls.
(edit)The genders have a lot to learn from each other, I will admit, but we also have to decide what qualities we are unwilling to relinquish. I think the ability to grit our teeth and banish thoughts of sorrow lest they sap our strength, is something men need to cling to with all their might. You may want to cry when the dragon burns your village, but the time for that only comes once you have sliced that pyromanic-reptile's head clean off, capiche?