Interesting points of view in this thread seem to be reasonable to me even when they seem contradictory. That is because there is no definitive response to the statement that "No pistol is good enough for bears." That is a clear cut declaration. But is it factual? No. I will make this statement: Any handgun is capable of taking down a bear. You could shoot a 44 magnum through a bear's outer ear and it will not do as much damage as a 22LR in the bear's eye. A 9mm in the face of a bear is going to be better than not being able to get a shot off with a rifle. Bears run at 35 MPH. That is just under 51 feet per second. How fast are you with the rifle compared to the pistol. Bear attacks do not generally occur at long distances. They mostly happen close up. A bear 100 feet away from you will be on top of you in three seconds.
Personally, I think the best defense against any bear is bear spray. Carry it in a chest holster or on a pack strap holster and you have a quickly accessible defense that can reach out to 35 feet and produce a wide cloud of 2% OC that will surely slow the bear down if not stop it or turn it away. Now you can have time to get the gun ready if you might need it.
There is a reason what National Park and Forest rangers carry bear spray. it works better than a gun. Their experiences proves that. Of course, nothing is guaranteed to work and so someday you might get the bear and someday the bear might get you. It is about odds, and bear spray is the best first line of defense in a bear attack. Everyone able to spray it should be carrying a canister in bear country. I mean everyone I the party unless they are to young to use it.
I live in PA, and I have hiked in black bear county for 30 years. I know black bears are wimpy compared to their big cousins. But when a 500 to 600 point male makes an aggressive charge it might a well be a grizzly. It can kill you just as fast. In 30 years I have encountered a few females making defensive charges intended to stop not hurt me. Defense is simple back out of the scene with bear spray ready. But when a male makes an aggressive charge it is another thing. In the two I experienced I never had to draw my duty size pistol. Bear spray simply worked. I stood fast and they ran.