It does more than that. It tarnishes the believability of all accusations of antisemitism, even those made by reasonable people about actual antisemitism.
It also proactively fuels antisemitism by conflating Israel with Jews more broadly. Because of rhetoric like this, some subset of people who are outraged at Israel l's actions will now direct that outrage at Jews more broadly.

But that isn't really the comparison being drawn. That comparison would be someone buying a shirt from a factory in a free northern state; because that shirt was produced by cotton grown by slave labor in the south.