He didn't blame them for being charmed and he certainly didn't kill off anybody that weren't his enemies either. Those that were 'better off dead' was a conclusion that he arrived at after interacting with them. Basically those that were fully charmed and betrayed/killed their friends and family around them, they retained memories of their actions after the charm was dispelled and deeply desired their own death out of guilt because they could not live with what they have done during the charm period. It's the same result the church and Apple got after treating people who were charmed. Keywords here are conclusion and result, they saw the victims and their reactions firsthand after the treatment of the charm, it's not just mere assumption.
You say he didn't give anyone a chance to heal? Of those that were charmed, Makoto killed those that were his enemies, left alone those that had no connections with him, and offered to help those that had. Haruka, one of the more significant character in the novel, was in the 3rd category. She was deeply charmed and betrayed her own country for Tomoki, knowing that she was the mother-in-law of one of his students, he wanted to save her by faking her death and hiding her in a base in the wastelands. Yet, she chose death of her own accord. It's fine if you don't like the novel or the MC, but you seem to be implying that the MC saw people who were charmed, imposed his own assumptions on them and killed them to 'save' them, that's false.
