You're wrong about Kosova, but in any case the analogy isn't a good one because, while in that case we did refuse to say "Stop the bombing", in this case we do oppose - not just in a general sense of not taking responsibility for, but immediately, sharply - an Israeli attack on Iranian nuclear facilities. The difference being:
- In the Kosova case, between a) the continued bombing and b) an immediate end to the bombing and victory for Milosevic in annihilating the Kosovars, there was no real lesser evil. While expressing our refusal to support, refusal to take responsibility for, distrust in etc NATO, we did not raise a slogan which could only mean support for one of the evils, "both of which were worse than the other" (Lenin's phrase I think).
- In the present Israel/Iran case, the status quo, ie no Israeli attack, is clearly preferable to an attack happening. We express our desire and we organise for a third option, ie that workers' and democratic movements in the Middle East can stop Iran developing nuclear weapons; but stopping an attack now is fully compatible with that goal. In the Kosova case, by contrast, the realisation of "stop the bombing" would have destroyed all the possibilities for our preferred option to emerge.