The opposing side counter-argues with really great points. The first argument is that Immigration may change or dilute cultural values or norms, but nothing suggests this is a negative. Many societies in the past and present have flourished because they have embraced new businesses, cultures, foods, etc. The second argument is that immigrants will flock to a country with a generous welfare program is all the more reason to moderate who we give welfare to, not to tighten immigration laws. The third argument, that immigration drains high-skilled labor from poor countries is real, but the possibility of migration to a high-wage country generates an incentive to acquire education.
If borders were open, many immigrants would seek out education in a different country but end up returning to their home country, knowing they could leave if they needed to. Temporary migration is common in many countries, and was common in the United States before the restrictions of immigration laws in the 1910s and 1920s. Finally, the fourth argument, that it takes jobs away from low skill workers and lowers their wages is combated with a simple statement, Only a bizarre view of equity favors people earning the minimum wage in rich countries over people near starvation in developing countries.
In my personal opinion, I think Immigration should be more difficult for some countries than others. I think we should reevaluate some of our systems. There are so many illegal immigrants getting FREE education and welfare without paying any taxes. This is a drain on our already struggling economy. Even though we are a global super power, we cant weaken ourselves by letting leaches into our country. We have enough problems as it is. I do think that legal immigration is a brilliant concept and should be more in effect. A looser border with Mexico might bring in a lot more drug trafficers and the drug cartel will probably move its way up north and establish itself in the U.S. All in all, I think immigration is a good idea, but has many things that would need to be heavily monitered.