Without showcasing his many years governing the Tol-n-Gaurhoth (Isle of Werewolves) it's impossible to fully know the role Sauron played, in his master's machinations. Warden of the Tower would have been at the forefront of Professor T's mind, writing. He was also Melkor's primary lieutenant, given command of the Host of Angband.

The miniscule amount of screen-time in LotR we get to see the Dark Lord in is only the "least trifle" in his entire being.

Nobody is going to cover 2M years of Middle Earth prehistory... that's the Silmarillion!

The PC police would have their hands full spinning both G'kar and Londo's rampant womanizing habits, way before Marcus showed up on the scoreboard. And then there's the very real problem of substance abuse from Mr Garibaldi and Dr Franklin. Let's don't forget that, in order to save the galaxy, an armed insurrection against elected leaders took place. Weapons of mass destruction are common, as is their usage. Prejudice and racism are woven into the fabric of society.

Marcus, as the author mentioned, was one rare, heroical tragedy due to his unrequited love for Ivanova. Upon his death, she mourned bitterly that she "should have at least boffed him once". Unfortunately, you can't change the circumstances to give him a happy ending (you pointedly left that option for resolution out) and at the same time succeed in showcasing his character as was. Same goes for making him fit today's PC mandate.