Both of these claims of Amanda Milius cannot be true: first, that we should save accusations of antisemitism for the rare times when it is real and important; second, that "everyone under 40" has been converted to anti-Israel, anti-Jewish rage through propaganda and lies.
It's worth noting that no one making claims such as this to warn and/or scare Israelis seems to be concerned with the serious problems such a constituency poses for the Republican Party and the US. So, either they're not serious, or they want to ride that wave.
It's very natural that people who are scared will try to draw others into their fear, to infect them with it, so to speak, in order not to feel alone in fear. Amanda Milius seems to me genuinely frightened, but one must resist contagion, and contain and cure the infection.
It may be that the NatCons and others have been using their own supply and genuinely believe that no US administration has ever been hostile to Israel. Vance seems, or pretends, to believe it. But other people have familiarity with the historical record.