He was a dentist. Nobody likes a dentist. They inflict pain. Even worse, he was a tubercular dentist. I'd conjecture that people may have feared his extraction forceps as much as his six-gun. And his cough, bloody sputumed cough.
If he was soured and alcoholic, well, I suspect a lot of dentists were (and are). Check out the rate of suicides by profession. Dentists typically top the list. It's an uncommonly high stress, perfectionist, singularly thankless gig.
Moreover, in those days the state of people's dentition and oral hygiene in general was a bona fide scandal. Quite disgusting actually. Enough to leave any dentist ill-tempered and down-in-the-mouth. (So to say.) Fluoridation of the nation's water supply didn't happen until the 1950s.There was no toothpaste, only tooth powder, typically a mix of baking soda, ground charcoal and god knows what miscellaneous else. Mass production of toothbrushes didn't happen until 1885. And then there was the infamously widespread "Colorado Brown Stain." Unsightly. And halitosis. Hell, Listerine wasn't even invented, much less widely used (that wouldn't happen until the 1920s), until 1880.
Add in the consumption, and no wonder the poor guy was soured. No wonder he took to the bottle and the gaming tables. The fact that he didn't commit self-murder is nothing short of a miracle. Mary Sunshine he may not have been, but he had every reason not to be.
As for his penchant for personal violence, that's easily explained. He was reared in the Deep South, at that time (and still, to an extent) a place possessed of a hair-trigger, quick to take offense, toxically masculinist culture in which physical violence traditionally not only was relatively commonplace, but often valorized. Then he finds himself out West, a hard-assed, rough and tumble place where physical violence again not only was commonplace, but often necessary for survival, especially for someone both physically weak, out of his element, self-medicating with booze, and who was mixing with some, how put it, fairly unsavoury types.
No, nobody likes a dentist. They inflict pain. As often on themselves as upon others.