The beauty is that this works for arguing for both sides:
1) What would have been of the US if the indians didn’t take pilgrims in? Therefore we need to help all the refugees.
2) Look at what happened to the indians when they welcomed their own doom. Therefore we need to reject all the invaders.

I’ll bet you a shiny 10 kopek coin the artist didn’t think of the second interpretation, and neither did most of the half a million people sharing the picture.

I guess that goes to show there’s really two sides to many a situation, and perhaps considering the opposing view would be more fruitful than figuratively calling the side you disagree with literally Hitler.