Are Immigrants good for the Economy?

Immigration has been a hot topic in the news lately. Massive demonstration have turned heads in DC. Monday May 1st has been declared National No Immigrant Day. What does this mean immigrants will not show up for work or school and they will not buy or sell anything. This is supposed to show the effect immigrants have on our economy. So how do they effect the economy. Some immigrants provide cheap labor, taking low paying jobs in construction, landscaping, custodial work, factories, and food services. Others provide provide valuable services in the fields of medicine, science and technology, and industry. No matter how you look at it, legal or illegal that are part of the workforce. Right or wrong they do help to lower production costs for products, and increase competition so that in the end the everyday consumer wins. What are your thoughts?