I think there has to be a logical balance to immigration and should be driven by social and economic needs.
Your graph plus the other posts on this topic implies that legal immigration over the last 50 years is too high. Our unemployment rate is 4.4%. How has legal immigration hurt this country or this economy? We face an ever growing shortage of doctors and highly skilled IT professionals. We are likely to face in the near future severe shortages of unskilled labor to fill unwanted, low paying jobs. (and no, Americans won't work in chicken processing plants or pick crops.) We currently see decent-paying factory and service jobs go unfilled due to a lack of applicants that pass a pee test. We need a well-constructed plan to balance immigration to US needs and not one based on keeping out the less educated, blue collar types.