That's probably true, given that people in America use more natural resources per capita than people in most other countries. All immigrants (legal and illegal) combined use more resources in the US than they would in their home countries. Illegal aliens often trash the areas they cross as they enter the country, which is also bad for the environment.
What I couldn't quite get from the article is whether this faction opposes illegal immigration, all immigration, or procreation. Are they just anti-people vegans?