Its hard though because in games you are generally the good guy, and the good guy unsurprisingly picks the right thing to do.
Mass effect is a good example Shepard is trying to SAVE the universe not kill it, renegade Shepard just happens to do it whilst being an utter c*nt. You cannot be Shepard and pick evil choices all the time, because then you are just being evil.
In my mind there are a few ways these things work
1.Games where you are the goody: Character makes positive decisions
2.Games where you are the baddy: Character makes negative decisions
Rpg's are a bit different where you choose what to do so
3.Rpg's where you are out to save the world (or save something) you are able to be a nob but your actions are ultimately just towards saving the world. That is the only kind of Rpg there is really. Unless you count Fable where you can literally just be a nob, but that is rare.
Rpg's where you are out to destroy the world dont really exist they are just the second thing I mentioned. There may be an element of choice but they are generally between two evil choices, or a slightly more grey choice, if the game is any good.
The Dragon age games are great examples
The Warden (DA:O hero): has to save Fereldan from the blight, he/she can be evil but everything they do is ultimately justified by saving Ferelden.
Hawke (DA2 hero): is rather ambiguous he is out to make his fortune, but you ultimately end up trying to save the city the game is based in, so that is really the same as any other rpg where you make choices, some are bad but all lead to a final good.
It comes down to what game you are playing, unless it gives you the choice to play as a TOTAL bad guy, then your choices can be negative but justifiable.