The way the rough draft is presented, the Jedi and Sith are both fearsome warriors. What makes the Sith dishonorable is that they serve the totalitarian Empire. A Sith who switches his allegiance to the cause of liberty is functionally equivalent to a Jedi.

Mind you, this is because telekinetic Force powers hadn't been invented yet by Lucas. Jedi and Sith are fierce fighters and cunning tacticians, but not superhumans. So there's no element of corrupting black magic attached to the Sith yet--that came later.

Once the Force became akin to a superpower, with light and dark sides akin to white and black magic, the Sith became irredeemably evil. This is reflected in their grotesque appearance: from the second draft onward, Lucas wanted the Sith knights to "look like Linda Blair in The Exorcist."

Also, the Sith in the rough draft are not stated to be an ancient organization like the Jedi. In fact, they may very well be a relatively new sect, created by the Empire in order to hunt down the Jedi.

In the backstory of the rough draft, the Jedi Order rebelled against the corrupt Empire, only for the Sith to crush the rebellion and hunt down the survivors. It's quite possible that the ranks of the Sith were filled by Jedi who remained loyal to the Empire.