It was pretty much survival of the fittest back then. Colonists did some bad things to the Indians, but they didn't really have some cushy life in the old world to fall back on. Many people came to this continent from Europe under the threat of starvation. Most from at least a background of abject poverty. When you are desperate enough to get on a wooden ship (many of which wound up wrecked in storms) and sail to someplace you know nothing about on the vague hope of farming in a climate you know nothing about, you just aren't going to be thinking of the property rights of weird (to you) indigenous peoples.