Why aren't men allowed to cry in our society?

I've wondered this a lot, and I've been afraid to ask this question. I am a grown man, but I still have a heart. I don't emotional or melodramatic, yet I do express sorrow. I was in the military during 9/11. Many of the people I served with were a bunch of insecure roughnecks. I couldn't restrain my feelings during the 9/11 attacks. I didn't weep rivers of tears, but it did make my eyes water. I had to leave to go to my dorm and let it all out. I'm sorry; I couldn't help it. Are men considered less manly or weak of they commiserate anywhere outside of a funeral? Is mourning a sign of femininity and a subtle loss of masculinity? I remember the famous like "There's no crying in baseball," by Tom Hanks in A League of Their Own. What about football? I remember John Elway and Bret Favre getting emotional during their farewell speeches. Magic Johnson did the same thing. By my definitions these guys are considered alpha males. I don't think most men would fight them in a dark alley. If Arnold Schwarzenegger or Vin Diesel's children were dying of cancer, would they be allowed to weep? Or would everyone expect them to put on the same tough guy facades they exhibit in their films?