“The spread of disease from European contact was not always accidental. Europeans arriving in the Americas had long been exposed to the diseases, attaining a measure of immunity, and thus were not as severely affected by them. Therefore, disease could be an effective biological weapon.”
Just because it was used on a few isolated occasions, but even then it was already well advancing on it's own. It was already a natural phenomenon.
The westerns saw the absolute devastation by their mere presences was causing unintentionally and occasionally decided to use it to their advantage purposefully...but I highly doubt that absent those occasions that we would have seen much different outcomes.
Absent total non-contact for the next two centuries...
https://en.wikipedia.org/wiki/Native_American_disease_and_ep...
The quote is from the section Disease as a weapon against Native Americans