You totally have your right to choose to recuse your child from a pledge. I'm curious though - what really is the harm in letting them experience different aspects of culture and religion? 

I've seen this kind of shielding backfire before is all. Think of it the opposite way: a parent who tells their child that drugs and alcohol are bad, but then they discover those things for themselves and think "Hey, this isn't that bad". Wouldn't letting them be exposed to different things help balance their perspective out a bit more? There are some really good aspects to religion. It's a mixed bag of course, but so are most things.