How were Mexicans treated before they got in the us?
They put up with a corrupt political system and as such end up having problems with law and order, then they bring their attitudes and values here if they sneak in the back door. When they come in legally, they learn about law and learn that they can be sent home if they don't obey our laws.
Mexicans do not hate white people! However, due to Mexico's problematic history with the US (i.e. the Mexican-US War in which Mexicans lost half their territory to the US) and other foreign invasions in the nineteenth century (i.e. France, Spain), Mexicans tend to be suspicious and guarded about "white people" and their intentions in their country.