Quote from HolyGrail:
All you have to do is apply to the government of the US to emmigrate here. It just takes too long to process the information.
You can apply to work here(green card) after which you can apply for permanent status.
You can apply if you have a relative in the US.
You can apply if you are an entepreneur in your country and would like to establish a business in the US or operate in the US.
You can request asylum in the US.
You can have a sponsor.
I'm sure there are many other ways as well. Unless you know someone that can get rid of the red tape you will be stuck for 5-7 years.
Now you know why they risk their lives to get here. If you have no hope where you are currently living you are not going to sit around in poverty waiting for something to happen.
I think it's great that people with "motivation" come to the US to better themselves and their families.
I have to admit my original question was somewhat rhetorical. I will try to address some of the paths to immigration you have suggested above, in particular as they might pertain to our hypothetical unskilled Mexican, who has never entered the US illegally or overstayed a visa.
"Sponsorship" can either be family based or employment based. A US person cannot sponsor an immigrant just because he feels like it.
Family Sponsored Immigration
This is the most plausible path for our hypothetical immigrant. Depending on the relationship of the sponsor to the immigrant, this process can take between a year and 23 (yes, twenty-three!) years and be subject to national quotas or not. The easiest case is that of marriage to a US citizen, which is not subject to per-country or global quotas. The marriage must be real and not one of convenience.
Employment Based Immigration
About 140,000 employment based immigrant visas are available every year. There are further per country limits within this number. There are several categories of employment based visas, with their own requirements and quotas within the total quota, which are outlined here:
http://travel.state.gov/visa/immigrants/types/types_1323.html
An examination of the above page shows that the only theoretically possible category for our unskilled Mexican would be the E3 category, but only if there are fewer than approximately 140,000 X 28.6% = 40,040 skilled degree holders with experience (roughly speaking) applying from the whole world for the year (let's not even consider the 7,000 p.a. quota for Mexico), which is a practically impossible situation.
Investor, Entrepreneur, etc.
The EB5 category is available for those potential immigrants who are able to invest $1,000,000 ($500,000 in deprived areas) in a business and employ 10 Americans. Needless to say, this is an unlikely category for our unskilled Mexican. Very few people apply for this category anyway, as the US is one of three countries which taxes the global income of its citizens, no matter where they reside. Wealthy foreigners are averse to this.
Asylum
This is a possibility if the immigrant can show he is subject to certain types of persecution, subject to many regulations. According to this article
http://www.guardian.co.uk/immigration/story/0,,1421580,00.html
the US granted 3,936 Mexicans asylum in the year 2000. Given the numbers and the requirements, this does not appear to be a viable path either.
The US immigration system is needlessly complex and, in my opinion, does not serve the national interest. The USA would do well to adopt a simple point based system like that of Canada for permanent immigrants, and a temporary work visa system for the millions of cheap labourers that the country seems to need.