Correction: the constitution was written with checks and balances because there are angels.

Think of it like this.

The creator created human beings (his children) and angels (servants). The angels were created to serve the children of the creator. But one angel, Lucifer, the servant, became warped and usurped the position of the creator because he could not, refused to, serve the children (Adam).

Originally, government is something that living men and women create in order to execute the work of management, aka governing. The government is in the angel position, and the people are in the Adam position.

This is exactly why government needs to have checks and balances. So that it does not go rogue and usurp the position of the people. Historically, governments have been the greatest cause of unnatural death (democide) and also have mostly been tyrannical in some form because they follow the pattern of the fallen angel, not good angels.

Ergo, this is why the constitution of the USA was written with checks and balances: because the government it creates on behalf of the people needs to be kept within its limited servant position, and not try to become the master.

I don't know if you subscribe to a biblical cosmology, and I do get it that you mean "people aren't perfectly good" aka "no angels" so that's why government needs to have those checks and balances, but I'm looking at this from a slightly different angle, not one that sees "angels" as perfectly good.

Which is related to why Paul wrote "do you not realize that we are to judge the angels?"

Wildly off topic, I know, but there you have it...