And here is a thought, every time you put in a fatigue report "post duty", you have just admitted you HAVE committed a criminal act.
Wrong. That would only apply if you said you were fatigued before flying but got on and flew anyway. I have filed reports when I became fatigued before TOD, although I felt OK before push-back. The fatigue report (at least ours) includes a section to report how you mitigated in-flight fatigue. Drank coffee, ate food, took controlled rest, etc.
If you feel fatigued during the cruise, on approach or taxiing in, or in the crew bus, you should report it.
But we must put the reports in otherwise our companies will think - and be able to "prove" - that their rostering is not causing any fatigue, or that heavy crews are not necessary, or 6 on 2 off rosters or 900 hours a year are sustainable etc. Pilots have a duty to their fellow pilots to put reports in.
If more than 50% of pilots were reporting fatigue, then something would have to be done.