cobb wasn't such a bad guy

Of course, that assumes that Cobb & Paden already knew that all of those others were dead. That's not something that we can assume.

Just because the audience already knows those outcomes before we see these two face off doesn't necessarily mean that the characters know. Heck, we don't even know that the events occur as linearly as they are shown to the audience. Once the "heros" split up to enter the town from different sides, those various events might very well be happening in parallel, more or less at the same time in different parts of town. (I know the town isn't all *that* big, but it's just barely big enough for that to be workable ...... Especially since a couple of the sub-fights are shown to be right on the edge of town on one side or another.)



As to the original question:
Cobb isn't *as* bad as, say Tyree (who seems more sadistic, one who would harm just to take pleasure from it).

However, he's not exactly good, either. He's perfectly willing to kill just as part of a job, without any concern for there being reason that might be considered "just". You look at a case such as Mal's father. His only "crime" was that he legally owned land that Cobb's boss wanted. Sure, Cobb would just as soon try burning him out and running him off first , but only because actually killings tend to create more problems. Once running him off didn't work, Cobb was just fine with killing him instead.

I'm sorry, but I can't consider Cobb to be all that good of a guy when he's doing things like that.