By this logic, I am stupid also. Not that I will lose sleep.
Its not so much on what he can do, but that he can providing moral support. By the same logic, why bother to go to someone's funeral? You are not going to bring him back to life, are you? Waste of time. If your argument is moral support, that people hoping president showing up (or at lest not play golf or swim at beach) is not complete r****d either (unless they think having president will magically make disaster go away faster).
But what do I know. I am stupid because I think its good for president to be present.
He would just be in the way. It would be much better for him not to be their and let the people who are trained for it do there job.