A problem with 'Evil' in scenario creation

Five years later and I'm back.   

For various reasons I wanted to get together a one-shot of "Love in the Time of Seith" (aka the crone game).  I was struggling a bit though because of the problem of evil.  Not the big theological problem of why evil exists, but the more practical problem of how to add adversity to a role playing scenario.

Of course, the traditional answer is that the DM's scenario provides the adversity.  There is some monster or evil villain who is the opponent.  The players are the good guys and they resist, explore,  investigate and defeat the enemy and his minions.  

Sometimes that's good enough.  The players buy into the scenario and everyone has a good time beating up on things. The scenario is something like "The mustachio-twirling evil necromancer with his zombie hoards must be stopped!"  Why is raising them from the dead and marching on our town? Maybe there is a McGuffin around that needs to be protected/destroyed or a prophecy that is being fulfilled. Who knows, who cares, grab your axe and have at them! 

Sometimes it feels rehashed and flat.  I don't want undead who hate all life because "undead" or an orc horde who murder, rape and pillage because the rules say they are "evil".   That's too easy.  It encourages the computer game solution of killing every character who is highlighted with the correct -- i.e. enemy -- color.  It is a cooperative game -- can the players use the rules to overcome some predefined obstacles -- but it doesn't give much of a story.  

Which leads back to Love in the Time of Seid (sorry, I'm not going to look up how to do the thorn character correctly).  There is no enemy.  No DM either, but mostly no explicit evil enemy to be killed.  The game is 5 characters with their relationships and is supposed to do from there like a Shakespearean tragedy (or comedy if you want, but the ending condition is two characters are out of play, so likely tragedy).  Unfortunately, one character is:

• a foreigner
• "middle-aged, fat and wily"
• a poisoner
• has Treachery as a main theme as is likely assumed to be treacherous
• controlling a spy in the King's court because he wants to take over
• the husband proposed for the Princess by the King, but whom she hates

Basically, the Earl is set up to be the bad guy.  Of course, all of that can be subverted, but if the other players focus on him as the villain there isn't much that can be done.  At least on the surface one of the players is being asked to play the equivalent of the mustachio-twirling necromancer invading the Kingdom.

Of course, the set-up  is more Shakespeare than CRPG so immediately grabbing a sword and attacking him doesn't seem fitting.  Besides, the resolution system doesn't make that a reliable option.  So that are more possibilities.  Still, I wonder if the player who ends up playing the Earl will feel limited.  (I played the Knight the one time I've played the game, so I don't know personally.)  Beyond that, I wonder if it would be possible to redesign that character so that he was less stereotyped "evil".