I think there are many reasons why the South African analogy does not apply to this case.
One, commonly overlooked, is that sanctions against South Africa did not become a really significant issue with a major impact until after years of education and organization had aroused enormous opposition to Apartheid, even in the corporate sector and mainstream political echelons, and certainly among the public. Corporations were coming to oppose Apartheid for business reasons. Mayors were getting themselves arrested in demonstrations. And so on. This was, in fact, all seen as an outgrowth of the mass civil rights movement, then peaking. When South Africa set up homelands (“Bantustans”) 40 years ago, it received virtually no support, only worldwide condemnation, even from its supporters (US and Britain in particular). When Israel does the same, it is largely protected from criticism, so much so that public opinion in the US on these matters — which is highly critical — is effectively suppressed and unknown, and within the media (including liberal media) and political arena there is essentially nothing. That tells us that there is a long way to go in education and organizing before it makes any sense to raise the issues of sanctions. In the current real-world circumstances, a call for sanctions, even if it were justified, would be greatly welcomed by the right wing extremists and hard-liners, because they could easily convert it into another “proof” that everyone wants to kill the Jews and so we must rise to the support of embattled Israel to prevent another Holocaust. People who do not pay serious attention to prevailing circumstances may cause serious harm to the people they are trying to protect. That happens over and over.
We agree that the Jewish population of Israel overwhelmingly opposes sanctions. To the best of my knowledge, there has been no meaningful call for sanctions among the non-Jewish population of Israel. So I think it is far to say that opposition to sanctions would range from substantial to extremely strong across the Israeli spectrum.
What about support for sanctions against Israel in the territories under military occupation, or the refugee camps in Lebanon and Jordan, say. I haven’t seen a study, but I’d be surprised if they did not support sanctions against Israel. I presume they would also support invasion and destruction of Israel. But I do not see what policy conclusions we can draw from that, apart from narrow ones: it makes very good sense to bar any aid to Israel that helps implement the occupation, meaning virtually all military aid and much economic aid. That is a principled position, and could be effective. It conforms to the majority opinion in the US even without the issue being publicly raised. Hence if this does not enter the political agenda — and it doesn’t — that is our fault, the fault of organizers, including those who focus attention on probably harmful and at best pointless issues like sanctions rather than on real issues where progress is possible, with plenty of effects.