I could argue with you, but I don't see what it will accomplish. The facts are that some will assimilate, but many won't. Furthermore, with enormous numbers, especially given PC politics, they're not likely to assimilate if the current rate keeps up.
Believe me, I'd like to paint a rosy picture on it, but I don't think that it will happen.
An astute observation. The Mexican (all Spanish speaking) legal & illegal immigrants/migrants have no incentive to assimilate as they are being accommodated in every segment of our society and business to be fully functional without even learning basic English which is the element that holds the multitude of ethnicities together as one nation.