How can you so easily agree that there could be flaws in the system, but then make such a definitive claim?
Anyways, not everyone agrees with you.
I'll refer you to volume 36 of the journal titled, "Electoral Studies - An International Journal on Voting and Electoral Systems and Strategy" in the section titled "Do non-citizens vote in U.S. elections?"
It can be found here -
http://www.sciencedirect.com/science/article/pii/S0261379414000973
They calculate that up to 2.8 million non-citizens may have voted in the 2008 election.
They also claimed that, "We find that there is reason to believe non-citizen voting changed one state's Electoral College votes in 2008, delivering North Carolina to Obama, and that non-citizen votes have also led to Democratic victories in congressional races including a critical 2008 Senate race that delivered for Democrats a 60-vote filibuster-proof majority in the Senate."
Who knows how many more non-citizen voters we had eight years later and how that would have impacted the primary vote.