It seems very difficutl to be evil considering that almost every hostile human encounter gives you karma simply for defending yourself from robbers, highwaymen, etc. Pretty much all quests give you tons of karma as well for choosing the best choices. I mean yea, you can be a dick and blow up gecko, or you can repair it for maximum xp/loot and vault city citzenship. Its pretty much a no brainer. Other "evil" choices like destroying whiskey bob's still are pointless because you can get the same reward for doing refueling the still, which also bumps up your town reputation. Joining the slaver's guild doesnt make sense either...given how easy money is to get and the fact that it locks you out of so many quests, including making Sulik go hostile. There are plenty of companions that wont join you fi you are evil, but i don't think there are any that will only join evil players.