But, the sheer amount of pie-in-the-sky idealization on both sides of the monarchist/parlimentarian debate beggars belief, and nobody seems to have called them on it. In some cases this might just be due to lack of relevant experience.
A common theme is that a strong executive (or royal prerogatives) is needed to combat the despotism of sectional and factional interests. To be fair, the Long Parliament was not an exactly inspiring example of how a single-body legislature would behave. But the notion that a king cannot diminish one part of his realm without diminishing himself is pure hogwash, and can only be written by somebody who has not really grasped the notion of "penal colony." Similarly, claims that a chief magistrate / governor would, by benefit of being selected by the whole state, be beholden "to no single faction or segment of society" can be made with a straight face only if you haven't experienced modern political parties. But these claims were made, apparently in good faith, by otherwise intelligent men.
On the other side, the idea that Parliament is able to represent the population "virtually" because it is large and closely resembles the voting public (so how could it harm itself?) has shortcomings that were obvious even at the time.
I am also somewhat surprised to learn, at this late date (considering my Christian-school education), that Paine's "Common Sense" spent a lot of time exploring Biblical condemnation of the office of kingship.