Thats an interesting, albeit absurd, claim.
What we did when we founded the country was legal in our eyes, just as what the immigrants now are doing should be, in their eyes, considered illegal.
I am sure that the Native Americans found our actions to be deplorable and, most certainly, had they the formal laws to illustrate the point, illegal.
History is written by the victors, and our grand actions were illegal, and indubitably immoral, when done to the Native Americans, and illegal, though not necessarily immoral, in regards to our actions against the throne.
So, there is no distinction between legal and illegal immigration if you are to consider our past, which your quote was attempting to do.