My supporting POV on selfishness motivating human moral values

[smax]

It literally has nothing to do with the Native American genocide.

That's just a failure on your part to properly consider the facts. The fact is, Lincoln coordinated and ordered assaults and conquests on Native Americans all throughout his term as President because, just like leaders who preceded him, he knew that it was vital that the "Indians" numbers and force continue to be reduced so that they would have:

#1. No military presence
#2. No political weight
#3. No significant hold over the land's resources

During Lincoln's term as president, he not only ordered attacks on Native Americans, he also broke numerous promises to them regarding land, resources, and money. He also ordered many Native American's to be held, without legitimate cause, in concentration camps. 

That letter Lincoln wrote, among other things Lincoln did, was so people like you could live ignorant of the reality of the injustice suffered by the Native Americans at the hands of European invaders/"settlers". Lincoln partook in Native American slaughter, just like every president who preceded him, but he did seem to understand the implications of the European conquest of America, much like he understood the implications of the slave trade, and he considered more than just the perception of his actions during the time, but also his place in history. That didn't stop him, however, from putting some of the finishing touches on the conquest of the American territory while also carefully maintaining important allegiances in Europe during the civil war. 

By the way, I have the same percentage of Native American ancestry as you, and I have close relationships with many of my family members and friends who are Native American. Not a single one of them celebrates Thanksgiving, nor do I. 

I mean, is it really difficult to figure out that something is fishy about a holiday that supposedly honors European settlers breaking bread with Native Americans and yet Europeans are relatively the only ones left around to celebrate it?

Chew on that for a minute.