"Yet still, a religious person could see it as idolatry."
In 1941, IIRC, a Jehovah's Witness student was sanctioned by a public school district for not reciting the Pledge of Allegiance -- for precisely the reason you just stated. The case was appealed all the way to the US Supreme Court -- and the Supreme Court affirmed the school district's actions. Over the next year or so, Jehovah's Witnesses were harassed, fired from their job, banished from schools, etc.
In 1943, one of the shortest times ever, the US Supreme Court reversed itself with a decision acknowledging its mistake.
Politicians and flag wavers conveniently forget that history. George Bush, Sr. conveniently forgot that history when he blasted Michael Dukakis for not wanting to require school students to recite the Pledge.
The Pledge, like our flag, aren't important in and of themselves. They are important for the values they stand for. One of those values is dissent. Something our "patriotic" friends ignore.