There's always a social tension between determining when an act should be formally outlawed and when it should be merely a social taboo. Generally its an issue that is best resolved by the communities the act appears in
Sure, this seems common-sense.
However, modern life tends to be such that there is no coherent community, or the acts of religious harrassment take place in public places (e.g. on the street) or in private (e.g. door-to-door proselytizers).
So in such cases, each person has to fend for themselves against the bully.