Don't discount the amount of common people that are totally onboard with killing everyone in another tribe. There have been plenty of times when leaders are the only reason diplomacy happens in the face of a bloodthirsty population, though certainly more common that war happens because leaders channel the energy of that bloodthirst as it is easier and the benefits (to themselves first, their tribe second) are thought to outweigh the risks. Look through history and you'll see enough instances of leaders trying to keep the peace only to be killed by their bloodthirsty population and replaced by someone who will act.
I wish we could all just get along, but so far the only effective deterrent in all of history has been the threat of destruction, either by a sufficiently powerful peace mongering leader, or MAD that nuclear weapons established. I suspect the next change in this dynamic, if MAD holds true, is some real AI that takes the reigns. It would be hard to rule break if we had an omniscient leader that could kill you within seconds.
Are you comparing raw dollars or percentage of property tax? Accounting for inflation and the increase of your property value? What about the whole situation where Texas collects the taxes but only disburses up to some amount to schools. Probably easier to just look at the ISD financials. Just need to remove all expenses for non education activities, like sports and administration. I wonder if the ISD funding also gets used to pay for ISD specific police. Just asking questions, without actually doing the work, betting teachers have lost way more than 30% in 5 years. Texas government is actively trying to prove that public education doesn't work so they can justify privatization, and bring back legal segregation plus religious schooling funded by taxes.