Rubio has been extremely consistent with his position, which is not pro illegal immigrant. He couches it in "pro legal immigrant" language, but he is not an open borders/amnesty guy.
Of all conservatives in the GOP, he is uniquely positioned to address the issue of illegal immigration, if it is going to be addressed effectively. I say that because it is a given the the demagogic voices that hound the GOP will hound him at every opportunity, and unfortunately, those voices hold sway in the debate. His heritage offers him some inoculation against the demagogues, and his articulation is second to none.
There are some who, from the perspective of a Latino, would sound harsh or intolerant. People like a Michael Savage, just as an example. In my opinion, Rubio is using the classic debate/negotiation strategy of legitimizing the concerns of those he addresses in order to convince them that he is "of" them, and therefore to be trusted.
I have no qualms about Marco Rubio. I'm glad he's out there, and I'm glad there is an articulate conservative Republican of Latino descent there to counter the lies.