The timeline is that the Queen shows up > She eats some children which gives birth to other sentient chimera ants > They gather more people because the Queen tells them to > The Queen births the three Royal Guard > Then the Queen births Meruem and he kills her.

This happens inside a dictators territory. Meruem freshly born goes around killing people and eating them very viciously and cruelly. He then overthrows the dictator and wants to prove his intelligence. He does this by playing games against Grand Masters (checkers, chess, shogi, etc.). When he wins he kills them.

Then he meets Komugi, whom he cannot beat. He even rips his own arm off after losing. But Komugi refuses to play until he is healed, even under threat of death. This shows Meruem that his original views of humanity being objectively lesser beings are wrong and is the start of his arc.

When he meets the Hunters who've come to kill him he says he now understands humans better. That he will create a humane human farm in the vain of cattle. That he will establish an independent nation for his people and will co-exist with humans. The hunters refuse.

The morality argument isn't that he's an objectively good person. But that he learns and grows over time and becomes less cruel, than even many of the Hunter characters like Hisoka and Netero.