The predictions by quantum mechanics of net vacuum energy and of slowing of ultrashort wave radiation by a quantum foam do not work out. This is because general relativity has theorems to the contrary. But why would those theorems win out? General relativity wins within the domain of its axioms, because a lockin theorem applies, namely the Bianchi identities that follow simply from the existence of the metric. It prevents the subject matter, spacetime, from experiencing alternatives to governance by the metric. Only where the metric can not be defended, on the small scale, can quantum mechanics overrule relativity with its theorems.
This dominance by relativity on large scales can even be nonlocal in the case of quantum foam. This foam can make as much mischief as it can in any small scale where the metric is not viable, but the theorems of general relativity intervene at some other location to require the opposite.
It is remarkable that a large scale effect of quantum mechanics does exist; the states of matter impelled by Bose and Fermi statistics are not overruled by relativity.
Michael J. Burns