Pledging allegiance to a flag always sounded like idolatry to me, with or without "under God":

"Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth: Thou shalt not bow down thyself to them, nor serve them..."

but I did it anyway, as a kid.