There are other groups, like Christian Science for example, which drugs and even vaccinations are not used. Christian Science does not because they believe that any illness is just an ill illusion of you mind. (on a side note they also believe that pretty much everything is just an illusion so I don’t see the reason why they bother gathering together when the building they are gathering in doesn’t exist, but that is off topic). In this practice, children are denied vaccinations that could be very helpful to them as well as medications such as insulin for children that are diabetic.
I may have to correct my post in the end-of-the-wold thread. I agree with Lexite on this matter.
It's a tricky social issue, but some religious beliefs clearly cross the line by endangering others who cannot make a decision on the matter. Christian 'Science' is probably the most obvious one. Lexite got it spot on - one of their beliefs is that all disease is an illusion. All disease. Including things like, say, broken limbs. Or cancer. Or diabetes. There's a number of horror stories I've read about Christian Scientists leaving their child writhing on the ground crying in pain for days after they broke an arm or something. Jehovah's Witnesses are perhaps the most mild example - refusing blood transfusion for yourself? Go ahead. Refusing blood transfusion for your child? Not so good.
Children don't have the capacity to consider religious beliefs in full depth. I know I certainly didn't really think about religion until I was 13/12 or so, and I had the benefit of being well educated, including religious education, basic philosophy, and basic epistemology. Anyway, the point is that kids can't possibly make an informed decision that they're a Jehovah's Witness, or whatever - they're far too young. In most situations, killing your child would be a crime - killing them because of your religious beliefs should be no different.
As for Scientology, I think everyone is aware by now that it's essentially a business masquerading as a religion (Rather like some televangelists, actually...) and benefiting from the automatic tax-free status religions get. They deliberately target celebrities - the buy-your-way-into-nirvana philosophy is probably pretty juicy to people with lots of money, too. They will stop at nothing to stop criticism of the cult - that's actually a directive from Hubbard himself - and are incredibly litigious. And well funded. And they are truly a cult - they encourage members to cut off contact with non-scientologists, they disbelieve in some aspects of established reality (I.e., psychiatry), and there's been a bunch of other shady practices around, too - including deaths of people in their custody due to negligence and the use of children as effective slave labour.
Far too many loathsome religions, far too little time. <_<