Still, I see no basis for discrimination based on place of birth, ethnicity, race, caste, creed, color etc. when I can do my job right and be good at it. I would agree that if it were a lottery or family based immigration, such caps could prevent chain immigration. However, employment based visas having that cap makes absolutely no sense and blatantly discriminates.
As for one ethnicity dominating the country -- the entire permanent resident visa program subject to the 7% rule is only 366,000 visas per year or .1% of the population. Even if all of those visas went only to Indians and Chinese the US would be in no danger of being "dominated" by one (or rather two) ethnicities. In any event on the family based side, which has a larger allocation than the employment based, it is Filipinos and Mexicans who face the longest waits, not Indians and Chinese. Finally the mapping between ethnicities and countries of birth is not one to one.