Well using ETs is not quite the same as the case in the Americas. One thing that's always been inevitable on earth is that those who explore overtake those who don't. In the big picture, even with all the small pox and syphyllis deaths, I still stand by my statement. Even in the most advanced remnents, in Mexico and Central America, they were cutting out the hearts of young girls to appease the gods, as recently as the arrival of the Euros. Where was what remained of civilization headed in the Americas? What would the Americas looked like circa 2005, if the Euros had never arrived, or, even if they had, had left the Americas alone? Think about it.
The Amerindians settled a 10,000 mile stretch of North and South America in a pretty short period of time. They don't explore?
For a variety of reasons largely having to do with geography and domesticable large mammals Eurasia developed oceangoing vessels first. It wasn't really a choice to "explore" or not, except in the case of the Chinese, who simply and deliberately chose not to.
Probably 90%+ of Amerindian deaths were the result of introduced diseases (non-deliberately) and no matter how the contact took place, it would have inevitably happened, sadly.
Go ahead and poke a little fun at the analogy if you will, but it is a good one, in this sense:
The arrival of Europeans on vessels that could carry 100 men, with weapons of steel and vests of armor, would have been as unknown to the Indians, as the arrival of Aliens would be for us.
And what would you think the arrival of a new culture to this planet would think of us. Specifically:
** We allow well educated men and women to cut unborn babies from their mothers womb and then kill them, just as they are able to sustain life.
** We have an entire culture of people who encourage their children to kill themselves, as long as they take others with them.
** We have had experiences, in recent times, where entire nations have grouped together with part of the result being the mass slaughter of millions of other people.
** We have had numerous governments organize themselves in such a way as to actively encourage the starvation of millions of their own people.
** We have millions of people here in the United States willing to vote for Hillary Clinton for President.
OK, that last one may have gone too far. But, seriously, you are trying to weigh the good against the bad. Not all Native cultures were the savages you are portraying them to be. And the death of 70% of their population through disease is a difficult one to overcome with the good things that have then happened.
The Spanish were burning people alive for witchcraft.
Some civilization..