I am not sure why we are having trouble with this concept. The "illegal" part has NOTHING to do with "residency". If you have been a resident of Texas (and thus paying Texas Sales Tax and Texas Property Tax) for the past three (3) years, you receive in-state tuition ... regardless of what the people in D.C. reflect in your immigration file. Period.
Any "non-Texans" who choose to move here for 3 years can also qualify for in-state tuition.
It has to do with the fact that they are being rewarded for illegal activity. I’m not sure why the Perrygasmics are having trouble with this concept. Perhaps if I explain it another way it might make sense. Imagine you (owner A) are part owner of a vast apartment complex. Another part owner (owner B) decides to rent out one of the units for much less than the going rate, exactly equal to owner B’s part of the rent, not sending any to the other owners. Is it any wonder that owner A wants nothing to do with owner B?