CA estimates 5-7 million in that state alone.
Keep in mind that in general the numbers of any anti-America protest are multiplied by 1.5 or doubled, and any pro-America are cut in half or unreported. Regardless of the actual numbers, it was a boatload of people.
One argument on the matter should be this: You say illegal immigrants just want to do the jobs Americans won't do and there is a need, fine, deport all the illegals and bar them from ever applying for legal immigration. Then for every one who is deported, this one time, we allow one LEGAL immigrant in. If there is a job to fill, and someone deserves to be here, it's the person that went the legal route, not the criminal one.
Of course, libtards and the illegal immigrants themselves will never admit that, so we kick them all out, bar them from ever reentering the US, and keep the same level of admission as before. When they complain, we just say we offered a different deal and they didn't like it, so we stuck with what we had and enforced the existing law.