Well, since many have false identification, and get jobs where they are paid by check, they ARE paying taxes. And whenever they buy something they pay sales taxes. And they get nothing for those taxes.
That's not all of them of course.
And the free ride is a problem.
An illegal has a child in the US, that child is by law a US citizen, entitled to an education, paid for by taxes. It would seem that the handouts are a major issue. But that's a drop in the ocean compared to the rest of the spending.
Illegals are replacing some of the labor in the US, but it's only select labor positions, they aren't "stealing" engineering, teaching, medical, tech, and other non-labor jobs.
There are certainly problems, but it's not as bad as some make it out to be.
I'd be far more worried about the $9 trillion debt. You want to know why you can't pay your taxes now? In the time it takes you to read this the US government spends $200,000.