Earlier quoted context omitted.
> justify the inordinate amount of money threw at them They're theorists, you're paying for pencils and paper. String theory may not have produced a theory of quantum gravity yet, but neither has any other line of inquiry.
sorta. the construction of particle accelerators has been justified to test the hypotheses of string theory
Particle accelerators have been built since way before any string theory was formulated.
The biggest and most powerful existing accelerator (LHC) has been built to fulfill the high energy/high luminosity requirements to explore the Highs boson energy regime (that has been found) and at most the lightest supersymmetric particles (not found as of today).
The Higgs boson is a cornerstone of the Standard Model. Supersymmetry is an extension to it that does not involve strings.