The anti immigrant groups argue that the country is too crowded and too polluted. That air quality is suffering and that there is not enough water.  Compared to what.  The USA is not crowded and will not be crowded if the population doubles again.  Even our cities are not crowded compared to cities in other parts of the world.  All of the problems that they mention are international problems and keeping pollution or a water problem in Tijuana or Mumbia is not solving it.  These are not national problems they are world problems. Allowing people to move where they want to in that world will help to solve all of these problems.  The accident of birth place should not determine destiny.
What the anti-immigration groups don’t mention in their ad is the effect on the economy of not allowing immigration. 

Imagine a store that was prospering and growing.  People wanted to shop there but the owners decided to not allow any new customers.  Would they continue to grow?

This is what a restrictive immigration policy does to the USA.  It is easy to understand intuitively from the store example how population growth creates prosperity but I think that we can see some correlation to the actual data available from the last 100 years.  
In the mid 1920’s the anti-immigration forces were able to dramatically reduce immigration and in the 1930’s we had the great depression.  In the early 2000’s we started to build fences, restrict legal immigration and the drum beat of anti-immigrant noise made newcomers feel unwelcome.  Now we are entering a major recession.
New customers are good for business and new citizens are good for the USA.  Numbers USA and their fellow traveller on the road to restrictionism are wrong and they hurt us all in the pocketbook.