I think your friend is right. I am on the other side of the country from... I live in New York. About an hour north of new york city and i've been hunting in the catskill mountains here since i was a kid. I grew up on Long island. In the past 5 to 10 years the bear population in my area has EXPLODED. Also the neighboring states like pennyslvania have always had a massive bear population. The reason is the great habitat, old oak and beech stands, blueberry thickets, and plenty of bogs and swamps and plenty of roadkill and deer for them to hunt. They get big up here too... most adult males will get up to 400 pounds easily. A lot get over 500-600 pounds and these 500-600 pound monsters frequent developments and suburban areas for garbage and domestic pets. Actually if you read back to 2004 a bear in the catskillls in a town called FALLSBURGH snatched a baby from it's stroller in someone's backyard and drag it into the woods... it made national headlines.
I think our friend is right, a lot of people understand black bears because of what is put out by popular tv shows like discovery channel and versus channel, which show black bears to be weak and small bears that can lose a fight to a squirrel over an acorn. I'm 6'3'' and 285 pound powerlifting, I can squat over 700 pounds and deadlift over 800 pounds and close grip bench in the low 400's, and I came upon a bear track a month ago that made my size 13 shoe look like a baby's feet in comparison. The point is that a 400 pound bear or 500 or 600 pound bear... while not a brown bear can still kill you. Most adult black bears are as big, if not bigger than a male lion or even some tigers.. though they don't have razor sharp claws they have that size and mass that is difficult to overcome without a modern rifle.
Black bears are born to be opportunistic and they are very curious and intelligent, they are like giant raccoons... they will eat anything that looks remotely edible. They eat EVERYTHING. Unfortunately sometimes a human walking down a hiking trail on a nice sunday afternoon may look edible to a black bear, especially if a bear has never seen people before.
A bear will atleast investigate a person before it gets scared, especially if it has never seen a person. Depending on how you react the bear will either run from you or try to eat you.
It is worth noting that a large adult male bear over 400 pounds is extra confident because of it's size and therefore has little fear of man unless it has been shot at or harassed by man before.
Your friend is 100% right if a mature adult black bear is chargin you full speed a 44 magnum will not have enough power and the bullet will not be big enough to IMMOBILIZE it.
Your friend is right and i'll tell you why, The key difference between a self defense weapon and a hunting weapon is that a hunting weapon does not need to immobilize the animal only needs to kill it... if the animal runs a few hundred feet its ok as long as he dies without a lot of pain, humane kill is all we're after here. But in a self defense scenario where a male adult black bear is defending his territory from you during the rut in early summer or trying to eat you, you need a big bullet of 400 grains or larger to obliterate all vital organs to stop the animal in its tracks.
Ideally you would want a brain shot if you can pull it off, but the risk of missing is too high, which is why you would want to shoot the shoulder bone and break it's shoulder to slow it down, then reload go for one more into the heart, then reload and put one into it's head if necessary. But with a .44 magnum the bullet is just not large enough and not fast enough to penetrate through the massive layers of muscle and bone.
for hunting a black bear with a .44 magnum, that is a different story... that you could do.. but it would not stop a charging bear.
Your friend is right that the animal may not realize he is hurt and keep mauling... just for example look at professional athletes or UFC fighters... some of these guys get hit and break there nose and don't even realize it because of the adrenaline
When the bear is attacking you he will be in "fight or flight" mode just like you will be, and he will not feel pain... all thats going through his head is to neutralize you and eat you if he is starving to death. Therefore you will need a weapon that will basically immobilize the bear with one shot.