- Mormon polygamy
- Christian sects that disapprove of medicine
- Ritual circumcision (especially when the mohel sucks off the debris from the penis with his mouth)
I would also add to that list the ritual slaughter of animals. Kosher and Halal both mandate that an animal cannot be stunned with a captive-bolt stunner before having their throats cut, and must be fully conscious. Needless to say, this cruelty only persists because of "freedom of religion".
If you ever want to get away with things you otherwise couldn't get away with, freedom of religion is probably the most potent argument you could unleash.