Am I the only one who thinks principles are more important than money?
No, but your principles are a modern invention. Slavery was a major part of the meditteranean trade with an essentially unbroken heritage going back to the Egyptians. Examples include the slave markets of Venice, involving Slavic peoples from Ukraine, the enslavement of Muslims after the Spanish Reconquista, and the slavery along the Barbary coast which was a matter of both Muslims and Christians participating. The Portuguese in the beginning followed the tradition that AmerindianHistorian layed out which was the trade of enslaved POW and Criminals with African monarchs. But when demand for slaves as sugar plantations grew, (in Sao Tome, Cap Verdes, and eventually in the Carribean and Brazil) slavery became much more industrialised and trade turned into exploitation. Christian or Muslim or Pagan would all have done the same thing given a reversed situation.
Imagine a man from the Future comes to you and says: "WHAT you exchange mere papers for the soul destroying labor of another individual?" If in the future a money less society that never works comes back and criticizes you for wearing a t-shirt made in China, or for paying taxes, or for not giving all your money away.
The fact is that one has to accept a degree of relativism when reading about the past. It is a very foreign country which had a different set of rules.