The idea of something existing “outside of space and time” makes empiricists nervous
This seems like a boring objection: where does the letter 'A', or the ascii 0x41, exist?
I'm willing to admit that concrete instances of both exist in space and time (and I might even admit maps forming a galois connection between those and the abstract ideal 'A') but there's no "reference" canonical A, located in time, located in space, giving them meaning.