And there is the movement in Berkely and other places. I suspect there may may be 10,000 people in the U.S. actively supporting BSD (albeit with a very generous definition of "active" that includes extremely small one time actions.) If 10,000 people are active than support is much larger than that. And it is not just happening in the U.S., but all over the world. So the cumulative affect is small, but not zero. "Stand with Us", the U.S. arm of the current right wing parties that rule Israel (as opposed to the right wing parties that used to rule Israel) is making opposing the BSD movement a priority. So they don't share your view of BSD as having no potential.
When Gil Scott Heron and the Pixies refuse to play Israel it apparently does affect the way Israeli's think and feel. It puts pressure on. The pressure is small, but any thing a movement does while weak has small effect. I described in the post you ignored that my acquaintance finds that it is actually promoting conversation among people in Israel who have ignored the existence of the Palestinians as anything but a threat. I don't know why missing the Pixies would open minds that ignore rockets and protests alike. Maybe because it is new, something that is not part of everyday Israeli life.
The fact that the effect is not zero is important. One way to build small amounts of power into greater power is to exercise what power you have to accomplish what you are able. We can't sanction yet, but we can boycott, and possibly eventually divest. You can't know that in the effort to fight that off Israel won't make more minor concessions as they already did in the face of people running their Gaza blockade.
Even very small concessions will make a difference in the horrible suffering of the people of Gaza, and maybe even to some of the suffering of the people of the West Bank.
And if it has any effect at all then this will be far more effective in building a movement to end U.S. support than just another petition to Congress. Look, Olympia has had more people active on this issue than most because of the death of Rachel Corrie, and the presence of Craig and Cindy Corrie who are some of the sweetest people you could ever meet. And everything has been tried. We have an unofficial Olympia-Rafah sister city program. We have had meeting after meeting with Brian Baird, and that has not been without effect. Baird opposed the Iraq war initially, but has moved to the right on most issues. But on this issue he has departed far enough from the standard Israeli line to be labeled by Haaratz as "consisently anti-Israel". And in spite of everything, the BSD has moved more people from fuzzy well-wishing to active support than any other tactic tried. (Of course it is only building on the foundation of all the other stuff that has been done. ) Yeah, 'more effective than anything else we've tried' is not a super-high standard. But should we revert back to stuff that's worked less well? And again, it is not like Boycott, Divest, Sanctions means abandoning other tactics. And contra Catron, it does seem like Boycott, Divest, Sanction has to be done in that order, just because that is the order that things can be implemented in terms of power. Boycott can be done by very weak movements, Divest by movements as they grow powerful enough to affect investing institutions, sanctions requires government power and if we ever get to that in the U.S. that means withdrawal of U.S. support, and no choice for Israel except a genuine deal with the Palestinian people.
As on most issues in the world right now, the good guys are probably screwed. But whatever small chance there is it seems like BSD is making better rather than worse. And from what Catron says, Heartfields accusations that UK BSD is focused on Jewish shopkeepers are apparently a load of bollocks.