There's lot of upside to electing more democrats - who eat cats - for the purpose of sticking people in office who In This House We Believe No Human Being Is Illegal.

Again, even if there's upside to electing more Democrats, there's virtually no upside to voting illegally if you're here unlawfully. Nearly all federal elections are decided by enough votes that it's almost no chance that any single person's vote will matter. At all. So unlike the endeavor of relocating to the U.S. - which confers enormous personal benefits on the person who does it - voting in a federal election provides virtually no benefit to the person.

And as for voting illegally - you people all claim it never happens, so who ever really looks for it? Only Republicans do, and guys like you shout them down for even wanting to secure elections.

Everybody. All the time. Almost all campaigns in contested elections will end up poring over everything to see if there's any potential problems with the election. People look for election fraud violations of campaign laws. Our entire system of elections is set up so that the candidates and campaigns can lodge these types of disputes - like the justice system, it's an adversarial system. The system is set up so that the balloting and canvassing processes are closely observed, the voter rolls (both registration and the list of people who actually voted) are publicly available and open for inspection, etc. Which is why election fraud and campaign violations come up.

What people don't find is any material voting by people who have crossed the border unlawfully. They find people that vote ballots that aren't theirs, that "harvest" ballots in a way that violates laws, people who vote outside of where they're registered, people who vote twice, etc. Here in Miami we had our own notable example:

en.wikipedia.org - Miami mayoral election

What they don't ever find is evidence that large enough numbers of folks who are here unlawfully are voting.

If this was happening on a scale large enough to matter, it would have been found. Even if only Republicans were looking, they would have found it. The process isn't perfect, but it is transparent enough that it would be easy to find.