In order to provide evidence for why Puerto Rico deserves to become the 51st State, the author arranges the text in a Compare and contrast style, drawing comparison to other state's situation like Hawaii or Alaska. One of these comparisons state that the states of oklahoma, New Mexico and Arizona were added as U.S. territory spread through the continental interior; or how the case of Hawaii provides glaring contrast to Puerto Rico.
Locke is trying to say that tyranny is the exercise of power for the wrong reason, basically meaning that it is abusing ones power over someone or something
I would've chosen cheap at first but then thrifty means being cheap and using it for a cause, not wastefully. So that's why it best fits that sentence. Hope this helps!