I'm playing devil's advocate here I want to explore ramifications. According to GR, geometry is dynamic. In string theory, 6-7 dimensions are compactified as a Yau-Calibi manifold. The properties of elementary particles depend on the topology of these manifolds. Presumably any gravitational curvature would change the topology of these manifolds so as to change the prorperties of the string worldsheet diagrams, making these higher-dimensional moduli unstable. Any change in these moduli, or even changes in the 4D large spacetime would change the string worldsheet diagram, which is in contradiction to observation. The strings themselves have a back-reaction on the configuration of the higher dimensional moduli, which would change the strings own properties as experienced as elementary particles. I am well aware that KKLT's proposal is to stablize and "freeze" these higher dimensions through magnetic fluxes and anti-branes. There's still a problem. If string theory were to describe the real world, the 11D spacetime would have be frozen and nondynamic, including the higher dimensions, b/c any changes in them would change the properties of strings and d-branes, which would change the properties of elementary particles, which is in contradiction to evidence provided to us by GR and the SM. String theory is the wrong approach to quantum gravity. What is needed is something like loop quantum gravity where spacetime is dynamic.