"God" to the Founders was whatever or whomever anybody wished to make of it, and was reference to the power, intelligence, or universal truth of the source of all that humankind was intended to be. Historically it was the power drawn on to do great things, to claim the right of life, liberty, and the pursuit of happiness unopposed by any despot, dictator, monarch, feudal lord, pope, or any other who would assign the rights to the people. And the Founders, pretty much to a man, even the Atheists, believed the Constitution would not work for any other than a mostly moral and religious people.
So the concept, sans any mandate of how one much view God and sans any mandate of how one must express his/her religious beliefs, is firmly entrenched in our foundations, our history, our motto, and our heritage. And for that reason, I have no problem with it being in the Pledge of Allegiance. Nor do I have any problem with the Pledge itself, because without allegiance to our language, borders, culture, we cease to be the America that the Founders intended.