I think ORMs are "inherently stupid" (or: "quite likely to be leaky as abstractions") because they don't necessarily share a theory with the underlying database

I think ORMs are "inherently stupid" (or: "quite likely to be leaky as abstractions") because they don't necessarily share a theory with the underlying databases ("something like but not exactly relational algebra") and I don't think many people spend time proving that the OO-like theories can be properly embedded into something-like-relational-algebra. Not saying you can't get work done with them, but it does mean that they're likely to leak.