Mat training instead of "no begging"

What is the big deal about expecting dogs not to beg? When I walk past a chocolate store I peek in the windows and my salivary glands are triggered and my senses are stimulated and my eyes get round ... why should a dog not have similar reactions to foods that tempt him?
Is it that they shouldn't look? Is it that they shouldn't act upon their impulses to take the food from our plate? Am I allowed to look in the store window? Am I allowed to look and see how much change I have in my purse? To buy? To eat? Chocolate!!!

Why do we expect dogs to have standards higher than those that we set for ourselves?

I consider begging to be a good opportunity to teaching a long reliable down stay behaviour!