1) coordinate acceleration from gravity doesn’t make one not in an inertial reference frame? 2) Why would something have to be in an inertial reference frame i

1) coordinate acceleration from gravity doesn’t make one not in an inertial reference frame? 2) Why would something have to be in an inertial reference frame in order for inertial reference frames to “exist”? Doesn’t make sense to me. In any case, that seems like just an excuse to ignore Lorentz boosts. One should address SR before addressing GR. 3) If spacetime were stuff, then it would be stuff always, not just when there are ripples or whatnot. But, in flat spacetime, you cannot describe it as a stuff in a way that is compatible with Lorentz symmetry, because the velocity of stuff changes under boosts, and so stuff can’t be stationary both when one doesn’t and when one does apply a boost. Therefore, it isn’t stuff.