"but even that was spread with intent once found out their immunity is weak against old continent diseases" This is somewhat unsure. First, if we are talking a

"but even that was spread with intent once found out their immunity is weak against old continent diseases" This is somewhat unsure. First, if we are talking about the Spanish conquest, that is deep 16th century, with all its magical thinking. God, the Devil and witches were all plausible explanations for epidemics, and holy processions, pilgrimages and carrying of medailons dedicated to saint X were considered reasonable treatment methods. It is a mistake to look at the 16th century with 21st century eyes; it is a different world resting on very different mental foundations. Second, at least in the Spanish territories, losing your workforce was economically disadvantageous.