Leftists teach the illegal aliens how to stay here, falsify a social security number, get welfare and subsidized housing wrongly, have the legal citizens pay for their children's education and get other government benefits that were supposed to be reserved for legal citizens. Further, the Left knows that these aliens will eventually become voters, who surely will repay the Left's efforts.
What you say here is as crazy as the the 9/11 is an inside job conspiracies. The massive number of illegal immigrants we have are a result of over 30 years of ignoring our own laws. A good number of them should be given amnesty and become legal citizens because most of them aside from the initial immigration have not committed any transgressions against us.

In the future we need to enforce our border properly and enforce our laws.

There's no secret 'leftist' training camps that teach people to do this, that's actually an illicit business conducted by very enterprising criminals and people smugglers.
As for the potential voters, by and large most hispanics are very conservative on almost all social issues from abortion, to the role of god in our lives and so on. They would by and large vote mostly Republican if the rhetoric on that side wasn't dominated by the extreme opinion of round up all the illegals and kick them out and then enforce shoot to kill on the border.

In regards to the school systems, those are not for 'citizens' but for legal residents. Even if those kids are illegal though it is to our benefit to educate those kids lest we create a further shadow society of people that in addition to other problems have no education.

Fifty million voting age U.S. citizens would never be allowed to move to Canada and take over. Stop playing bells and whistles and focus on the real core issue.
If over the next several decades millions of US citizens moved to Canada illegally and the Canadian government continued it's current lackadaisical policies then they'd have a similar problem.
We however are the nation that shares a border with Mexico and as such must enforce that border.