My problem is that we cannot agree on even the most basic concepts, like “love”, “murder”, and the like… I have been around for more than 10 years, and never could establish a common ground, on which we could strive to reach an agreement.
And what’s a pity to me is that it sounds like you might have wasted ten years trying? That is, wasted because if your goal was to try to pull Catholics off the rock of Peter where the dogmas are preserved, you never
could have found the common ground you were seeking, unless you stepped onto the common ground of the Rock, or you pulled someone off the Rock into the shifting sands.
As you note, Catholics have a
permanent position on what constitutes murder, that cannot be changed (even by a pope). Whereas you start from secular grounds (and then apply a rational process), we start from, or are at least open to, religious grounds (and then apply a rational process). It’s possible for sincere, well-meaning people to come to understand whatever internal coherence there is in another person’s argument – but still to reject it because there’s a starting premise which the two parties disagree about. (E.g. “There is a God.” “There is no God.”)
Rational argument
does not require that every dogma be explained on merely “secular” grounds. That’s not what rationality means; rational and secular are not synonyms.
As it is, these forums are closing. So one way or another at least the unproductive conversations can come to an end.

I hope you enjoy a wonderful and fruitful holiday season ahead!