I think that everyone should learn about ALL the major relgions in the world, whether they are Christian, Muslim, Buddist, Hindu, or Athesist or agnostic.
However I think that religous education should be taught as "This is what Christians believe" rather than "This is what WE believe". Children should not be subjected to attempts to convert them to different relgions, but they need to understand and tolerate difference. Ie. Learn that there are times that we should agree to disagree.
A basic knowledge of the five world's major relgions helps children understand current affairs, history and avoid offending people from other cultures to themselves.
If parents want their children brought up as a Christian, Muslim, athesist or pagan then they can take their children to church/ Temple/ Mosque out of school hours.
I like the assemblies at the the special school I work at. They have no relgious songs, but the school has fun singing pop songs. Although the songs are non religous they have lyrics encouraging good behaviour.
All the children are included and gain from the experience.