Human Rights Watch has accused Israel of needlessly and recklessly exploding white phosphorous munitions over civilian targets during its recent Gaza campaign last January. Israel claims that it did not violate any human rights norms because the shells were used for legitimate military purposes (smoke screens). The problem is that there are other types of munitions available that produce smoke screens without the harmful side effect of incinerating civilians (slate has an excellent explanation of phosphorous munitions). HRW also claims in its report that the Israeli military was often nowhere near the white phosphorous shells when they exploded and therefore could not possibly benefit from any screen they created. Additionally, the munitions were exploded over targets that are normally considered out of bounds (they were detonated over a school and a hospital). It seems that these weapons were used for the purpose of killing and harassing Palestinian civilians.
This logic leads to two possible explanations: harassing Palestinian civilians with incendiaries was part of the IDF’s strategy or it was a result of the IDF’s frustration at their inability to prevent Hamas from firing rockets into Israel. Personally, I cannot fathom any strategic end that would be served by firing incendiaries on civilians (especially since the best way to prevent people from firing rockets into your country is to make them like your country). It seems then that the Israeli army used these weapons against civilians out of anger or vengeance or just plain frustration. Possibly they assumed that the Palestinians were going to be their enemies no matter what course of action they took, and firing incendiaries on them for questionable military applications seemed inconsequential from their perspective. Indeed, Israel made use of the fact that “Western armies” (I read this as the United States) use white phosphorous all the time for various military applications, and no doubt they feel reasonable safe knowing that the US will help them dodge accusations of war crimes.
Israel also responded to the accusations of HRW by stating that Hamas should be charged with war crimes for using rockets against Israeli civilians. This finger pointing only makes it more obvious that the IDF is frustrated and that it is (possibly) lashing out against the Palestinians for the indiscriminate attacks on Israel by attacking the Palestinians indiscriminately. I doubt that their approach will reduce the number of rockets fired into Israel.