Btw, based on this episode it's reasonable to assume Ryner doesn't even know what manner of a man Tiir Rumibul really is. He never witnessed him emptying villages or massacring indiscriminately. All he actually has seen is the dude fighting against soldiers attacking him and not even killing too many of them.

There's a distinct difference between his own level of aggression and Tiir's, only a blind man would fail to notice that, but that's just a personality quirk. Since he's himself faced persecution, it would be natural for him to assume Tiir might have faced even worse, thus explaining some of his actions (that Ryner knows of).

So, saying he would take the side of a monster by joining him is now still highly premature. Right now he just took the side of somebody just like him: one called a monster by the normal humans. You can hardly blame him either for desiring company that isn't suspecting him all the time and from which he doesn't need to hide his true self.