I get the historical parallels, I just don't get how the people in the show don't. Its a few hundred years in the future, but you'd still think that people would notice whats going on and protest. There seem to be absolutely no checks and balances to the power of the corrupt in EarthGov. At this point, if it goes any farther, EarthGov will start making the Alliance from Firefly or the Empire from Star Wars look like superior governments.
To be clear, my annoyance with EarthGov isn't effecting my enjoyment of the show. Its just a bit annoying to learn that, in B5, humans are actually worst in general then they are nowadays. I hope the EarthGov stuff doesn't become too muddled in reliving the past. I get it, JMS read a history textbook once. Either tone it down, or go full facist/dictatorship (which would atleast be something different). Still, the mediocre EarthGov stuff in no way messes with the rest of the show, which more than compensates for having to deal with an annoying EarthGov related character or plotline every so often. Also, I can see the earthGov stuff eventually going somewhere interesting, its just not there yet.
Yeah I can't answer much of this without getting into spoilers, so I'll try to keep to generalities.
First off the idea that a society shouldn't or couldn't repeat the mistakes of the past rather flies in the face of the evidence. The examples I cited are just *some* of the most notable examples of the last century. We've been repeating the same stupid patterns for all of recorded history...and probably a while before that too. In short, it's not that humanity is "worse" than it is today, it's that it's just the same as it's been since we climbed down out of the trees and invented boredom.
As for the inner workings of EarthGov, it's probably worth keeping in mind that most of what Clark is doing is actually quite popular back on Earth. Even now, most of the human race still lives on Earth and most of them (around 10 billion) have never been into space, or seen an alien outside of the vids. Most people's opinions are going to be coloured by past experience. For example: First Contact was with the Centauri who swaggered into Earth orbit making themselves out the be the grand high overlords of the universe...an image that was quickly dispelled as soon as the Narns were encountered. The only other race to have significant interactions with Earth was the Minbari...who tried to kill everyone...and were very good at it. Needless to say neither races exactly engendered much in the way of trust and good will. Something a character says later on in the show sums up the attitude of most humans fairly succinctly: "Aliens fighting aliens? Doesn't really concern us now does it...?"
Human colonists are rather looked down on by the general Earth populous; Mars born in particular are considered ungrateful upstarts. Even more so recently since the colony declared neutrality during the Minbari War. The result was an EA military governorship, trade sanctions, food riots (which Sheridan helped put down) and of course the open rebellion at the end of season 1. With all that it shouldn't be at all surprising that most humans are more concerned with domestic issues than foreign policy.