Hang on - are you saying these activities aren’t motivated by religious beliefs? Sure it’s the extreme, but it happens, has happens and CONTINUES TO HAPPEN enough that I agree it’s not appropriate to say “religion is purely a matter for people to consider how to act on themselves”. If people could keep their religious views to themselves and not apply them to others we wouldn’t be in the world we are, and this entire topic of discussion would be irrelevant, but they can’t so we have to work from there.
Even without referring to mainly historical religious activities, what about killing people for witchcraft? There is a trial underway in London RIGHT NOW because a couple killed a relative for being possessed by evil spirits and practising sorcery. Turns out it’s not the first time they’ve tried to do it either. This kind of action is fuelled by religious and superstitious belief, and letting people have at it leads to these kinds of results.