A reminder, the MC is a child, in this latest chapter he's probably 14 y/o. In his previous life, he was sickly and died in hospital before he was 20 y/o. So, of course, he had not developed much in terms of moral in that aspects. I feel that his pacifist view is more along the line of: they were a small group who lived hidden on the island used by the church to exile children. The MC wants to stay hidden to keep rescuing the children, while slowly looking for his family.
Also, the fact that he didn't "kill" the slave traders now lead to him being able to remove the slave collar and gain another powerful ally, who know Kaede personally and wanted to help.
Even now, the MC probably still think that subterfuge and secrecy is still the best policy to keep everyone safe, for now. I am look forward to when he need to expand his territory and what will he needed to do. And he did get called out that he lack conviction. I am interested to see how will the MC develop even further.