No, I didn't miss the point. The point is that cross contamination is a serious problem. Actually, the Spaniards, and the rest of Europe, were lucky the Native Americans didn't harbor some fatal, contagious disease their immune systems couldn't handle. The European's understanding of medicine in 1520 was no better than the Aztec's understanding of gunpowder. If Queen Isabela had understood the risk she was taking for her people, I think she would have had second thoughts about sending Columbus (especially with everything that was going on in newly conquered Spain). On the other hand, we have had over 500 years of experience in cross contamination. We have a fairly good understanding of biology and medicine. Just as the European explorors protected themselves as well as they knew how, we also should protect ourselves as well as we can before we venture out. To do otherwise would needlessly endanger not only the bold explorers we send out but also the rest of us. I, for one, think we can afford a conservative, deliberate approach that lands us on Mars as soon as feasible with minimum risks.

Dave M

BTW: If the Aztecs had had the technology to launch and invasion of Spain, They most certainly could have conquered it. You can't cross the Atlantic in canoes and you can't build caravels or galleon without metal tools. They would have easily and quickly adapted to horses and the Spanish arquebus was far too cumbersome and slow to have been a factor.