Sure, but “effectiveness” is usually not a binary and is often difficult to measure. Small, but persistent changes should still add up. Eventually.
So long as people recognize that these things are in fact quite toothless, I’m not sure they are entirely detrimental. There’s no reason this couldn’t be used as a starting point for more effective action, now that signatories are in greater contact with the campaign.
Are you trying to equate the ideology of a political regime with a minority population of South Africans?
South Africa had no right to exist as an apartheid state, and Israel has no right to exist as an apartheid state.
After apartheid ended and living conditions improved, black South Africans didn’t go and slaughter every white South African as retribution, so when Israel says freed Palestinians would slaughter all Israelites, why should we believe them?
If the occupation ended today and Palestinians were allowed to live fairly and given ample resources to rebuild, what reason would they have to seek further conflict? If treated fairly, why would Palestinians act any differently than the South Africans freed from apartheid? This conflict is ultimately the direct result of unfair treatment after all.