It's not porous, in fact silicone is probably one of the best materials for keeping water IN something, but it's so good at it that is just basically traps water forever in any tiny gap, making it mold city.Not where I originally read it, but https://lifewithoutplastic.com/silicone/
It's mostly safe according to them to. There's no real evidence, it's mostly hypothetic.
I was wrong about the porous part though, I did remember wrong. But the others got a good point about food getting stuck.