Why, so they can flood our system with crime and violence? Do we really need more weed, cocaine, heroin, and meth in our country? Most of that comes either from Mexico, South America, or portions of the Middle East. I don't want it here.
Nor do I want our native population replaced--nor do I want political correctness laws to be even more extreme than they already are. Do you really want it to be "offensive" to use terms that actually refer to common items (such as a popular vegetable) because they are taken as slur for people from certain countries? Or, do you want to have to speak Spanish to accommodate them? Everything will be required to be in Spanish--so they won't have to learn English to live in a place where English is the official language.
And, illegal immigrants as a group are the ones that are lazy and have bad work ethics. While there are exceptions to this, most of those would try to enter the country legally instead of sneaking in (along with their 18 kids so they can have a sob story about getting in, and another one to gather welfare and drive up housing costs for the rest of us). They also tend to drive wages down, because they will work for piddling, displacing native workers and forcing them also to work for piddling. If that's what you want, by all means support illegal immigration.
Otherwise, they should all be deported, sob story or none (and that might dissuade others from marching their 200 children through Mexico just to present this sob story). And, unless you want to abandon English to learn their Spanish, nothing should be in Spanish. They want to legally immigrate, they need to learn our language and to become fluent in it, not having us needing to become fluent in their language. As is, aside from major tourist cities along the border, I am tired of seeing everything in Spanish far away from the border or any Spanish colonies (such as in Florida). Why I should be able to read Spanish to a degree just from this, without even trying, just because illegal immigrants refuse to master English.