Coxswain said:
Because they're not "evil" and "benevolent", and it's not even really shades of grey. They cocked it up in ME1 by making most of the big choices very clearly good/evil, but it's pretty apparent in ME2 that Shepard is almost always intended to be a good guy; Paragon and Renegade are mostly about how you do good things, not whether you do good things. You're Renegade when you're abrasive, decisive, and unforgiving. You're Paragon when you're friendly, cautious, and willing to let things go as long as the solution is a net positive. It's entirely possible (and frankly, more realistic than "hold up-right" or "hold down-right" Shepards) to be proficient at handling different situations in either of those ways, as the situation warrants, without feeling like an inconsistent character. That's what the Paragon and Renegade meters represent. It's a big step forward for video game morality, as far as games with morality meters go.
In ME1 it was severely broken. Picking paragon meant you were a self-righteous ass and picking renegade meant that you were a Sociopath (and racist). I cannot stress how 'meh' this system was, it was pretty discordant if you oscillated 'tween the two stances.
ME2 fixed ME1's problems, as both sides are now more centrist and as you say, if a meter must be used, it is best that it is NOT a zero sum game(Unless we are talking Dragon Age Loyalty, that was the right choice for that game)
I still have issues with the system though (other than the fact that metering morality/ethics is stupid).
The main problem I have is that I do not believe that a meter is needed at all. In some ways, ME forces you to pick a side, as you need enough points to go through some checks.
The biggest issue is with the consequences. Since every scenario has a guaranteed Paragon/Renegade way to get out, you can chose either side in confidence, and know that you will resolve/persuade the other party. The system could best be optimized if sticking to your morality means that it could get you into serious trouble.
Ex1: Trying to stop an unstable person from killing himself.
P: Your life is not worth throwing away
R: Stop whining and man up
As things are now, both methods could get him down. But since this dude is unstable, P is the best option, while Renegade could/should possible crack him.
Ex2: Dealing with career criminals
P: You could do better things with your life, right all your wrongs. Imma let you go so you can do this
R: Mofo, I am not letting you go. Either you rot in a cell, or you rot right here with a hole in you brain
The paragon option SHOULD backfire, as reasoning with criminals in that manner is only asking for more crimes to be committed. While the renegade option of sending them to jail or their grave be more effective.
There is also the fact that if P/R is about reputation, then the consequences of scenarios should play just as much a role on how paragon/renegade we are as the initial choice.