@FiveLinden
To the OPs questions:
I’m not sure if you are going to get an answer to completely satisfy you, but if you are looking for more of a historic explanation rather than so much an explanation that is morally and emotionally satisfying, I would say this:
What made Christopher Columbus famous in Europe & Europeanized America was his discovery of the Americas. That’s it. That’s why there are cities, territories, and even an entire country named after him.
If you read about Albert Einstein, he was pigheaded and cold towards his wife, writing to her (in exact terms) that if she wanted to be with him, she would give him three square meals a day, iron all of his clothes, and leave his room whenever he wanted on demand without expecting or anticipating any affection from him. But Albert Einstein isn’t famous for being a cruel husband. He is famous for his breakthroughs in physics.
The Knights of Columbus is a little more complicated. It was founded by an Irish priest in the 19th century in a time when newly-arrived Catholics were frequently persecuted by the protestant majority. At that time there was widespread questioning of their loyalty as Americans, since the Pope was paralleled to being a monarch, and Americans were not friendly towards monarchy in addition to the religious divisions between protestantism and the Church. In light of these challenges, one of the facets of the KoF is “patriotism”, and it was a form of ecumenism with mainsteam protestant society; it was a way for Americans to see Catholics as members of their society and not enemies. (And yes, ecumenism did exist and was practiced by saintly figures long prior to its more official elevation at the 2nd Vatican Council).
I would agree that these original motivations have to a large extent expired or have at least been altered in the 21st century United States. Catholics are fairly well accepted & established in the country, and Americans aren’t adversarial towards monarchy like in the past because it is a more-or-less obsolete subject. But in the 1800s, these were both still extremely hot-button issues that needed to be addressed. This is in addition to the fact that the KoF has spread beyond the eastern US and has long since been a multi-national organization.
For what it’s worth I entirely agree that it isn’t an ideal name, but I wouldn’t expect it to change, at least not in the near future, if for no other reason than because it is already such a well-recognized brand.
If you were to become a Catholic, you would of course have the latitude to disagree on the issue of Columbus. As a body of over 1 billion, there is a considerable amount of variation based on people’s national origins, backgrounds, etc.