The immigration debate is a far more varied and complicated thing than many Americans realize. That has been evidenced by the way Bill Gates and other leaders in the high-tech industry are reacting to parts of the Senate bill that would limit the number of visas granted to foreign workers who are skilled professionals.

This is the opposite end of the debate from the one that concerns illegal immigrants streaming in from the nation's southern borders. It has little to do with undocumented noncitizens using tax-supported resources and everything to do with an attempt to protect American workers in high-tech jobs from legal immigrants with skills.

But at its heart lies the same emotion — fear.

The United States has retained its strength through the years because of its ability to renew itself regularly through immigration. In many ways, the nation retains its leadership role in many industries because it attracts the best talent in the world — people seeking to work in a place that values and rewards hard work and innovation.

This traditional role will become even more important in coming decades as members of the so-called "baby boom" generation retire. Without robust immigration, few people will be around to replace the jobs left vacant, and the burdens on programs such as Social Security and Medicare will be great.

According to a report this week in the New York Times, the Senate immigration bill would take away a company's ability to sponsor workers needed for specific jobs. Two senators are sponsoring an amendment that would gradually phase out employer-sponsored green cards over five years. Meanwhile, the bill would raise the limit on H-1B visas, which allow temporary employment for people with university degrees or special skills, but not to the level many American giants, such as Google and Microsoft, would like.

Some people worry these workers drive down the wages of American workers who have the same skills. However, in a competitive world where emerging nations are becoming serious threats to the U.S. high-tech dominance, companies need more freedom to attract the best and brightest.

There are many fears surrounding all facets of immigration. It has been thus from the earliest days of the republic. But the biggest fear should be that Congress would put too many limits on immigration, which has been the secret to the nation's continued prosperity.