@ShinGetsu your excuses are really lame.
-That's fair enough, but he shouldn't have shown himself in the first place. Super retarded move. Not killing her after leaving was the cherry on the top of the fail cake.
-Since he's already been framed, he should kill them both. There is no difference at that point. None whatsoever. He could also easily go to any other country with his MAX stealth, seeing as almost nobody can detect it.
-Considering the many opportunities the MC had to kill both the King and the Princess already, even in the very first chapter, you're reaching too hard here.
-In my opinion, Japan is not peace-loving at all. Going by their cultural manifestations (not only manga), it's pretty clear that they are really all about honor and single-mindedness, peace not really factoring in when it conflicts with their current focus.