I agree that legal immigration is an absolute necessity if this country wishes to flourish but for a different reason. Without immigration and fecund immigrants, the US is not sustaining its own population. There is not a single economically-thriving civilization in all of history without a burgeoning population. Just look at Japan and most European countries. They have had to allow Muslim immigrants in because they are at a negative population growth. The fact is that the US that we have known (white, Christian, manufacturing based) is over. The only hope for the US of the future is to pass on the values of the Founders and hope for the best.
Passing on the values of the Founders will not be possible unless we have a long pause from mass immigration, just like we had from the mid 1920s until the effects of the deceptive 1965 immigration reform act took effect.