Russia assisted India with its nuclear program to kick Pakistan for its support of anti-Soviet forces in Afghanistan. Russia considered retaliating against Israel for supplying arms to Georgia with SAM deliveries to Syria. Syria offered to help Russia retaliate for the US ABM deployment in Poland by allowing a Russian one in Syria. Israel bombed a Syrian nuclear reactor with North Korean consultants. Russia sells ABMs to Iran to counter American expansion in the Middle East.

The difference between offensive and defensive weapons is artificial. Israeli offensive aircraft is used for strategic defense. Iran uses its strictly defensive SAM to protect its nuclear offense capabilities.
Can weapons suppliers be held responsible? If so, by direct attacks or by arming their enemies in a quid pro quo manner? What if quid pro quo is not available: Syria threatens Israel’s very existence with Russian weapons, but Israel cannot arm Georgia sufficiently to wipe out Russia?

Rules and justice exist only on a micro-level, among people, because people are about even when compared to the overwhelming law-enforcement power of states, and interactions among them conform to statistical patterns. In international relations there can be no rules, because the subjects are highly uneven, the interactions are too few, and abstract rules therefore cannot be developed. In foreign relations, Israel has to hit as hard as she can in every particular case, and disregard the screams from abroad.