I don't see why everyone is taking sides.
Old guy wants to protect his country, and has sacrificed people to protect them.
Rash young hero wants to protect his friends.
The two sides both have people they want to protect, and it just so happens their goals clash with one another.
The quote from @WTFits takes place in chapter 53 of the sequel, Majo no Geboku to Maou no Tsuno.
This whole prequel is a build up to that quote to emphasize the suffering both of them have gone through.
It is well worth the read.
After reading the prequel, it really is cruel.
Sauro was debating about bursting in to save Arsenyo from the torture but knew he wouldn't manage to get him out, so at the stake was the only chance.
But that was when Arsenyo (after holding out from torture to avoid implicating Sauro) gave up...
It's not even a devil @Knighto. Just a sapient creature that wants to survive just like anything else.
And, it's ok! Arsenyo becomes Nyo-Nyo and it's all good!
@Doomer do you think if the merchants were assassinated the former lord would bother actually finding evidence? He'd just accuse the main character and put forward some false witnesses saying "yeah I saw the MC personally execute the grain merchants".
The Former Lord can always make up a reason...