"Perhaps you are not ready to admit that the geometrical relations of Minkowski's spacetime are a construct that arose from (Poincare) synchronization."
Of course not. Because it didn't.
"Initially I didn't have any problem with Einstein's SR except for it ignores that the past is different from the future."
As organized in one's mind. Nature, however, is indifferent to the distinction.
"However, when I read the 1905 SR paper, I couldn't swallow the idea that a synchronization between A and B which are moving relative to each other can be directly reached by means of a signal from A to B and return. My reasoning tells me that in this case the distance from A to B differs from the distance return from B to A and therefore the two time-spans are different."
Only at relativistic distances and speeds. You are trying to apply Newtonian reasoning to a relativistic model.
"Relativity belongs to distances because there is no preferred point in 3D space. However, since the actual moment is obviously the natural reference of actually elapsed time, there is ubiquitously only one time all around."
Right. All physics is local.
"Relativity of time is not justified. I criticize the principle of 'relativity' as misleading."
So, in fact, did Einstein. He recognized that special relativity is in fact a theory of the absolute (the speed of light).
"I suspect a coordinate-free representation in this case a method of self-deception because it tacitly hides aspects of reality."
What aspects of reality were hidden before Descartes, when all geometry was done free of a coordinate system?
Best,
Tom
