Oh lord, spare us. Your side makes out that it's just a slur aimed at the Israeli government, and then you complain that it's also used for other Zionists! Lots of people call expansionists "Zionists", not just neo-Nazis and "Islamists", although they are well represented as doing so on Google. And few people would use the phrase "Zionist terrorists" who aren't so describing the government and armed forces of Israel (and it's true that the combination is unlikely to be much seen in mainstream work, because it's rare that governments of any kind are described as "terrorists" in mainstream publications). But the phrase is used, and it is used by people outside those mentioned. And it's not necessarily true that it has "fallen into disrepute" (more original research  you simply will not source any of this stuff, will you?) so much as it has never been much used. I don't doubt that. There are relatively few "Zionist terrorists". Given the nature of terrorism, that's hardly a surprise. There aren't many American terrorists either.