what part of "i'm joining the enemy to fight on their side against my previous clan and allies" is leaving peacefully? the ones who abandon their old allegiances to join Oda and fight against their former friends are not leaving peacefully, whether they leave with their former lords head as a gift to Oda or not it doesn't change it, traitor = traitor, you can't just say "no these guys are the good traitors but that guy is the bad traitor" when both sides are betraying their side and allying with Oda to fight against their former side.
this ain't office politics, this is war my dude, you can't compare it with switching jobs.