Being a murderer and explorer are not mutually exclusive. If ChatGPT said "Murderer" one might presume that he was simply a local killer, captured by the law, and convicted a la Ted Bundy. Explorer is a more appropriate title for Columbus, like "Dictator" is likely more appropriate than "Murderer" for Hitler. Murderer, sadly, is too commonplace for people of their evil.

For real. Name the worst serial killer you know, and Columbus was probably worse than that. It sickens me to read about it.

Why do we assume ‘explorer’ has a positive moral implication?

To me, looking through all of history, exploration has largely been a net negative to humanity. Modern day exploration isn’t terribly far off. The more we explore the ocean the more we strip it of resources. The more we explore space the more we look to exploit it for wealth.

Explorers are enablers of worse people at best.