Perhaps Bob is a keeper of peace and not just plain evil.

 Black Lodge: Another Place

White Lodge: Twin Peaks

Cooper told Albert that Twin Peaks was a place where the yellow sign still meant slow down, not speed up and so on. Twin Peaks was a quiet place according to Jean Renault until Cooper arrived.

Laura soiled Twin Peaks with her lifestyle and had to be stopped. Remember what Jacoby told Bobby, "Laura wanted to corrupt people". Everyone involved in the drug buissnes got killed in different ways by different people but to kill Laura Bob needed to intervene himself.

Windom Earle soiled Twin Peaks as well, but as Bob knew he wanted to find the Black Lodge and use it's power for himself he waited for Earle to come to Bob. It was very important for Bob to kill Earle instead of letting him take Coopers soul. But when Cooper had enterd the Black lodge it was also essential to replace him with his dubbelganger. What goes on inside the Black Lodge must be kept secret.

 Also, Josie meant to kill Cooper as he was one of them who had turned things inside Twin Peaks. But for some reason Bob didn't want her to kill Cooper so he took her instead.

Point: Bob is a protector of "Another Place" and "Twin Peaks". As long as Bob remains Twin Peaks will still be that quiet little place on earth.

Laura was damned and could see Bob, perhaps she mixed her dreams with Bob to much with reality. And she saw what would happend to her in the future many times before Bob really raped her in reality.

Perhaps Bob's real task was to guard Twin Peaks and Tha Black Lodge. But when Bob started to disobey, they sent Mike to stop him.

Twin Peaks just seemed to be a quiet little place. There was drug abuse. There was a father molesting her daughter. There was several other bad things happening. Cooper's arrival brought these things to daylight.

If there is a war going on somewhere, it doesn't mean it's peaceful if someone says "all is fine" and doesn't let anyone to see the facts. That's what Twin Peaks was. No-one wanted to admit that the prettiest girl in town was a drug user and a prostitute and it was all influenced by Bob. Bob has been feeding on fear and suffering forever. I can't see him being as a protector of anything (expect something like the protector of the right to be immoral. and i'm not meaning immoral things such as doing a small shoplifting or lying. I'm meaning things like child abuse and murdering people. If someone would protect the right to buy and produce childporn it would be Bob :D ).

I never took Bob as real as such, but more saw him as a physical manifestation of the evil some could see in people.

I also thought that the whole series was steered in the 'all pointing to Cooper' direction so I do see the 'everything was fine in Twin Peaks until Cooper arrives' point, especially after the Jacque Renaut comment mentioned earlier.

Worth noting, the Autobiography Of Dale Cooper may or may not reflect the darkness in Cooper.