The founding father's were mostly deists, not christians. The puritans came seeking religious freedom, not the other colonists. And part of this religious freedom, is for the government to not impact the practices of any religion or lack thereof. Bringing the christian god into the schools does this.
As far as the pledge, it loses nothing from removing the words, it even reads better in my opinion, "one nation indivisible, with liberty and justice for all". Our nation is not "under God","heavens","sea gulls" or anything else.
And I don't think anyone has ever said scrap the pledge, just remove the words to change it back to a simple oath, not Christian advertising.