Columbus was heinous even for his own time — and this was recognized by many people, including the Spanish crown. Many things in 1500 were accepted which are not excusable today, but to call Columbus' actions consonant with the morals of his time goes too far.

(And while the Middle Ages aren't exactly my specialty, I'm pretty sure Hitler was evil even by the standards of 939 CE. I admit I'm not drawing a line at 1940 in making that assessment, though.)

Otherwise everyone before 1950 would be evil.

The fact that things widely seen as unacceptable today were often less widely reviled in the past does not negate the existence of those who eschewed and condemned them even then. Nor has moral advancement, by whatever definition, been monotonic.