So many folks in here are going out of their way to shit all over something they don't understand.
These men do what they do to honor the memory of others. They view the performance of their acts in the heat, cold, and rain as a tiny bit of self sacrifice to pay back the sacrifice of so many others. The guards are a symbol of American dedication to courage, remembrance, and honor. They aren't so much guarding the tomb itself, as they are actually guarding the memory of the fallen. As long as they are there, others will never forget the selfless dedication of the honored dead that came before them.
If you crossed the line to put a cup of hot anything in their hand, well.....you wouldn't do it again.