For about 150 years locos were changed, vehicles added by a pilot loco, emus joined up, etc, without any issue. No PA (because there wasn't one) to sit down, no locking of doors (because you couldn't), and what is more, in the train you never seemed to even feel it. This included emus which were driven directly on arrival into contact with the unit ahead, no prior stop, with passengers ready to alight. Never a problem.
If someone can tell me that reversing a steam loco from a cab with no rear lookout onto a train, often at night, with just a gentle kiss, is somehow easier than driving an emu with all mod cons, I will be interested to hear it.