Caba,
I think a key point to deal with is the continuing, repeated calls.
Yes, that is a key point.
If a householder has told the JWs he/she is not interested they should not be subjected to continued visits everytime the territory is worked. Therein is the harrassment.
Exactly. Why should anyone have to put up with that, a persons religious freedom should not be allowed to interfere the rights of others not to be harassed on their own door step.
Is it the householder's responsibility to formally request relief?
No, I don't think so. It should be taken for granted, that unless the house holder requested a visit, and they belong to another religion it is harassment to call repeatedly uninvited to talk about religion.
Could the JWs (or other similar groups) be required to ask if future calls are welcome? Would it be illegal to require JWs or other such groups to ask this?
I think it should be fair and not single out just the JWs, same should apply to all religious groups, especially those that do it on a regular repeat basis. Why should a person be continally forced to resist such tactics when clearly their home privacy is being invaded, by a bothersome religion they don't even belong to.