I've no idea whether Spaniards and Englishmen really did find Indians unfit for slavery but I guess the argument that is being made is that more of them might have been kept alive if they were able to provide greater economic value to their conquerors. Sick, I know.
Agree that it's not an opinion fit to be voiced in modern society, however, it doesn't seem to be the opinion that people are trying to cast it under.
[0] https://www.reddit.com/r/IAmA/comments/4bxf6f/im_curtis_yarv...
Oh, well, that makes everything better.
Being enslaved is an awful fate but it is a hell of a lot better than being slaughtered because your oppressors can't find a use for you.
However, I don't think misconstruing his words is a good attack. The dust eventually settles.