Basicly I agree with you. But just maybe Nigel Owens knows how Parisse must feel at this moment in the match and in his career and decides to take this into account and therefor lets this one (walking away) slip. If so, it makes him an even better, at least more human, referee in my opinion.
Both Marler and Lee handled this case examplary and very mature. Too bad World Rugby had to intervene. The message I deduct from this saga: if you do something stupid, don't feel sorry and don't try to solve is as two adults. World Rugby will slap your ass with a big fine and a suspension anyway.