Dear Dr. Minguzzi,
Reading your Essay is a joy. You have this utterly professional skills to elaborate on the most intricate issues in GR -- the obvious, and deeply puzzling, fact that we observe mass with one "charge" only.
May I ask a question. You wrote: "Instead, only massless particles make sense, and thus the concept of non-singularity must be expressed from the 'point of view' of massless particles."
I wonder how you would explain the absence of Closed Timelike Curves (CTCs) from the 'point of view' of massless particles. CTCs are exactly what we should expect from GR (cf. W.B. Bonnor, Closed timelike curves in general relativity, Int. J. Mod. Phys. D12 (2003) 1705-1708; gr-qc/0211051 v1). It seems to me that CTCs (and timelike naked singularities, cf. R. Goswami et al., gr-qc/0410041v1) are just like the ultraviolet catastrophe from 1905, which too has never happened.
Thank you for your (global) time.
Dimi Chakalov