When you listen to many of the aguements - there is little differentiation between "legal" and "illegal". People complain about the language, they complain about the culture, they complain that their cities are being ruined but the truth is, most of them can't tell the difference between an illegal or a legal Mexican immigrant, and there are plenty of legal ones. That's where the bigotry comes in. Even if they are legal immigrants, they should learn English and make an attempt at assimilation. This isn't just about Mexicans, it is about all immigrants, legal or illegal.
In fairness though - the pro-immigration side often fails to make distinctions between legal and illegal immigrants. They don't make distinctions because they don't want people to know there is a difference.
Regardless though of whether they are legal or illegal - they are still people and deserving of certain minimal rights.
Except for drug traffickers maybe.