The person I'm replying to isn't talking about "rationalists" in the sense of Descartes and Spinoza, they mean the people in the Bay Area who read Eliezer Yudko

The person I'm replying to isn't talking about "rationalists" in the sense of Descartes and Spinoza, they mean the people in the Bay Area who read Eliezer Yudkowsky and talk about AI safety. And those people are not Platonists in the least. If anything, the usual accusation levied at them is that they drift too far in the nominalist direction. This is evident in pretty much all their writing, so I'm wondering where the GP is getting the impression that Platonism is their intellectual original sin.