I thought fast-math meant (among other things) that the compiler could algebraically simplify things using some rules for real numbers that don't apply to 32-/64-bit floating point numbers. I'd expect that reducing the number of operations would more often than not reduce the error due to rounding, which is what most people would want when they talk about "correctness".
Which step in this (very naive) argument is wrong?
Which step in this (very naive) argument is wrong?