See, trifle, this is where I disagree.
'I dont call it respect, I call it shoving your beliefs on others'
Normally, you would have a choice about whether or not you entered the place of worship. Admittedly, things are a little different on a school trip, but still. By allowing people in to see how they do something, they are hardly forcing beliefs on anyone. What they are saying is 'Look, if you do want to come and have a nose around to see what goes on here please could you follow our customs'. I think the rabbi was being very accomodating - essentially saying 'It is more important to me that your child tries to develop an understanding of a different world view than that he wears a hat.' Fair play to him, because you were not big enough to turn it round and say 'It is more important that my child understands that people don't always see thigns our way than that he has to wear a hat to do it'.
I think dismissing it all as 'mumbo jumbo' is just as dangerous as being forced to mindlessly follow a religion. It all leads to a complete inability to understand one another,and this is precisely why wars are started. It's not the religion itself, it is a complete lack of understanding or empathy for what anyone else has to say. Let the kids go in and hear some of what each religion is about. As long as they get a number of differing viewpoints, they will in the future be able to have rational, fact based opinions as to why a particular religion is the way it is.
If you don't like it, stopping kids from going on a trip allows bigotry to persist - you don't get the chance to see that someone who does things differently can still be a decent person. Which is precisely why I cannot abide religion in any shape or form.....
(Just to put the cat among the pigeons, it is not so very different to saying to other children 'My house, My rules. You may not do this at home, but this is how things are done here!!')