In the olden days drum brakes and pudding basin helmets killed a lot of guys. If the brake is set up incorrectly several things can happen. If the backing plate is wrong it can cause the situation where there is too much self-servo and the brake might not come off immediately after braking, so the bike remains stable and steers itself off the road. If the leading edges of the shoes heat up and become sticky, on the second braking the brake can lock at the slightest touch and launch you. If you set it up to be finger light to get quicker response, you need to stay in practice so that you don't inadvertently grab a handful. If you are using it a lot you might need two different linings so that you've still got brakes at all times.
I have crashed all over the landscape due to drum brakes. A disc brake is a much better option - you have none of those problems. In Australia we have an historic race class which requires the bikes to have drum brakes. The good brake often costs as much as the motor. They should be banned - thankfully nobody uses pudding basin helmets these days, so at least one part of the fatal combination is not there.
When I started racing in the 60s, I crashed at about the first 5 meetings, and once about 4 times in one day - all due to the drum front brake. Just before I finished racing, I locked my 7R AJS brake and went down the road on the top of my head at about 70MPH. Thankfully I was on my side when I reached the ripple in the bitumen. I still have a dislocated chromo-clavicular joint, however the accident was really a potential killer. These days my Seeley 850 has two Suzuki discs with AP Lockheed calipers up front with asbestos pads, and a single cast iron disc on the back. I can stop it like hitting a wall without crashing and it has to be that way. Everything about the bike is light and quick - handling, braking, acceleration. NO CRASHES !