The problem I have with pure renegade is that such a person would never, ever climb to the position Shepard's in and will rise to.
I have that issue too.
However, experiencing Pure Renegade can be interesting.
It does show that he's a 'Chaotic Violence' individual, who in a different setting with a different threat, would be totally out of his league.
But against an overwhelming enemy force, he does give an air of someone that everyone would be forced to submit to, as their better. Instead of Paragon Shepard inspiring others to think they stand a chance, Renegade Shepard puts the most emphasis on him as a valuable asset. And well, at least in the story we're shown, he is. He's the Reaper killer.
When you go Pure Renegade, many don't even think kindly of you, and it shows in ambient dialogue. What they *do* seem to think of you more than Paragon though, is your ability. They submit to you more not due to your behavior and helpfulness, but because you just look like an outright powerful being. Reputation follows Shep since ME1, and Renegade Shepard can and does capitalize on that.
I can buy that. But only in the specific situation everyone is written in. They're lost, not really ready for the Reapers, and chaos can allow specific individuals or entities to rise to the top, if only for a while. In this case, it is Renegade Shepard and the Normandy. Just don't expect people to have your back afterward.
I agree that Renegon and Paragade (at least in ME1/ME3, for ME3 you just bring a lot of Reputation along) are the best of both worlds. I think that for most of the trilogy, it is even designed that way. As long as you have one of the sides maxed out, you're good for 'full' story progression, but having the other side strong can make things very enjoyable.