Bringing in low cost foreign workers to maintain a system directly drags down the average wage, hurting Americans in the IT industry and lowering their income & benefits. Foreign workers are a tool that companies like to use to scare IT workers away from organizing & unionizing, keeping the Americans they do employ under foot and poorly paid.
As an example, Kroger has a support center for its Fred Meyer brand of stores in Portland, OR. As of last year, they were paying $12hr while expecting in depth networking knowledge, familiarity with SUSE & SunOS, and the ability to write moderately complex scripts for these legacy systems.
Comparatively, another employee who was transfered from Portland to Cleveland went from making a little over $14hr to $120k a year, as the market in Cleveland is apparently so barren of talent that poaching is a serious issue.