Sorry for the misunderstanding.. you are correct a birth certificate is not acceptable ID for travel... but it is generally required to, and makes it a lot easier applying for a passport, which is required to travel internationally anyway, and is the best ID one can acquire.  
  I certainly disagree carrying a passport ( or the smaller card they offer as well I think) is anywhere near "extremely cumbersome".  What`s extremely cumbersome is misreading a law and finding yourself and family  stranded at an airport and unable to board a flight you had planned for because you didn`t read the fine print.  
In the 40`s fighting Hitler everything was rationed,..you name it.  We are at war with a stone age ideology coopted by uneducated zealots by the millions and we don`t have a draft, or ration a thing...
 Carrying a passport is not so bad a thing to help assure safe travel for the rest of us. And god bless the greatest generation.