It makes perfect sense but I'll go slower so maybe you'll understand this time.
The wealthy and the large corporations pay the vast majority of taxes in this nation.
The middle class pays a relatively small amount even though it is the largest group and uses the most services.
When someone makes very little money, their tax burden is almost nothing. They still use the same amount of services that someone making much more uses. Roads, schools, etc.
The meager contributions they make do not come close to paying for what they use up. This means that if use is not going to be decreased, you have to pull the money from somewhere or stop offering the services.
If the illegals can't pay for it, that means someone else has to which means either higher taxes (which hit the middle class the hardest) or a reduction in services.