Elizabeth Warren's ancestor was probably just following orders.
I have no American Indian ancestry as far as I know, but I did have relatives who were on the Trail of Tears--a distant cousin married a Cherokee woman and went with his family on the Trail of Tears. I find their descendants in the records as late as 1907. Some of them spoke only Cherokee despite being partly Scots-Irish in ancestry.
The whole point was to establish their credentials as good citizens to prevent just the sort of tragedy the 1838 Trail of Tears became. Sort of like the old white guys in ObaMao's America who paid their taxes, fought our battles and kept our noses clean only to be told to get in the back of the bus because we are now a threat.