Can anyone really operate these things safely anymore?
Well, 40+ years of "post-steam era" steam operations with 1 boiler failure is a pretty good record, though I'm sure we'd all rather it be 40+ years with no incidents at all.
Certainly they can be operated safely. All it requires is adherence to existing safety rules and procedures and the constant exercise of vigilance, good judgement and common sense. All of which were sadly lacking at the Gettysburg. Neither of the firemen knew how to properly blow down a water glass, and it turned out that the engineer didn't, either, in spite of his years of working on locomotives. They had gotten too complacent with working on a locomotive with only one partially functioning injector, no lights, etc. It had been going on for some time, and finally caught up with them.
Any endeavor will always have a few people who will work harder trying to evade rules than to simply obey them. Any endeavor will have a few people who haven't a clue what they are doing.
No endeavor is or can be made 100% foolproof.