People are afraid of it because of the huge number of accidednts that have happened with it in the past. Exploding boilers can rip buildings apart quite easily. I did a repair job in a unit where the water heater, a very small inline unit, exploded. It embedded chunks of ceramic from the housing in the wall fifteen feet away and sprayed the bathroom with boiling water. If a child had been in that room, which was a distinct possibility in this case, they would probably have died and definitely suffered severe burns.
Big industrial boilers have multiple layers of safety mechanisms built into them to prevent incidents. Even small ones like several I used to maintain for some honey extrators have two or more redundant safeties to prevent explosions. A home built or antique unit ... not so much.
There are plenty of antique stationary engines that would do the job just as well and have far less risk.