"A man convinced against his will is of the same opinion still"
If your boss doesn't care, then no amount of begging, pleading, or cajoling will get anywhere with him, and even if you could force a change, it wouldn't turn out well for you, as you'd create a scheming bad boss, instead of just a bad boss.
Your best bet would be to quantify the cost of his behavior, and then lead him down the right path with the Socratic method of teaching.
Wow Boss, we lost 5 people so far this year. How much do you think it will cost to bring new people up to speed?
Hey Bosss, this turnover is costing us X in lost productivity. What do you think is causing this?
Hey Boss, If morale is so low that we are losing people, should we do something to correct course?
Hey Boss, do you think there is anything you can do to boost morale?
Not those words, of course, but the idea is to plant the seeds of change in his head, and let him come to his own conclusions, and change course himself. If he cares at all, he will, if he does not, you have not directly confronted him.
This approach is most likely to work because any ideas for positive change that come will come from his own mind, which he will not push back against.
What should we do
tends to get better results than
You should do this
Another approach that works is to simply ask for help.
Hey Boss, can I get your help on something? We keep losing people, and it is hurting our productivity. Can you help me figure out ways to retain them?
You cannot beat a confrontational person by being confrontational. They have far more practice. This is a kind of verbal jujitsu, taking his energy and redirecting it towards a positive goal.
Try it, at the very worst, you will be no worse off than you are now.