"I think that it's impossible for RE to be taught at schools without bias. I know I had Christianity drilled into me at a supposedly moderate primary and secondary school when I was young. Conversely I know a devout Muslim RE teacher who has no time for Hinduism and Christianity, I can hardly see that he can teach 'neutrally'.
Also, I disagree with many of the principles in various religions, such as sexism in most (no female bishops, pope and cardinals men, burkas for women, anti contraception etc), plus sacrificing animals and other things I find offensive. My concern is that religion is thrust upon my child with no criticism given.
As I said in my op, I don't mind a brief overview being taught, but I object to brainwashing that all religious principles are decent and without critique. I'd say leave it out of the curriculum."
You seem to have a lot of preconceived assumptions about how religion is taught in schools. DD is 12 and is at high school, they have assembly, but they don't have religious assemblies. There is no Christian bias at her high school and she has one hour of RE a fortnight. I would hardly call that overkill.
I expect that the way religion is taught has changed a lot since you were at school.
As for many practices of various religions I doubt that the teacher will condone them, they will just be taught as "this is what they do". I don't agree with some of the practices especially the more barbaric ones like circumcision for example, but I am not going to prevent my daughter from learning about it because I think she needs to know. Plus she is quite capable of deciding for herself that it is a horrible practice.
You can ask for your children to be pulled out of assembly at primary school, I am sure they won't be the only ones. And can I suggest you talk to the schools you are interested in and ask about how they teach religion. It strikes me that you are slightly afraid that your children are going to be brainwashed into joining a cult.
I also think that leaving RE out of the curriculum is very short sighted and bigoted. Learning about other religions helps us understand about so many customs and teaches religious tolerance.
Sorry, but I think YABU and haven't thought it through properly.