The letter writer assumes that the working poor of the suburbs are pitted against the working poor of the city in a zero-sum struggle. He assumes that adequate medical care for the urban poor, or for prisoners and addicts, can only come at the cost of inadequate care for his family and other suburban families like them.
And...well, exactly. If you're in power, you maintain your grip on that power by making sure that the people below you are perpetually squabbling amongst each other, rather than banding together against you.
Hm. I might have to write more about this later.