Funny that. My last problem was when my reserved Upper Class seat became a Premium Economy seat too.
The trouble is when a problem happens, as a passenger you're backed into a corner. You can't threaten to transfer your custom to a competitor - even if there happens to be another service you know you'll never get a seat without paying an absolute fortune. You can't threaten to cancel the whole thing because generally people are travelling for a reason and have to get somewhere. There's nobody to complain to who can put things right for you - sure you might get to talk to a supervisor but they're only going to spin you the same line - there's no aviation ombudsman or someone who can make them give you a seat on the flight. You can threaten never to travel with the airline ever, ever, ever again, but you know they don't care about one individual and they know all airlines are the same so it's a hollow threat anyway.
So the passenger is feeling backed into a corner. The airline holds all the power and the only thing the passenger can do is argue their case and hope to get things changed. The trouble is that the adrenalin's already flowing and some people are really not very good at putting their case. You see it every time you check in - someone's late or their bag's overweight or they've been bumped onto another flight - and they're standing there arguing. It's not surprising that occasionally it boils over.
Don't get me wrong - I'm not defending it or anything - I'm just saying it's not that surprising.
So BA's reaction is to go even further and say:
Now if YOU argue too much and WE judge you to have been rude then WE're not going to let you fly at all. Oh, and by the way, the check-in deadline applies to when you have received your boarding pass for the flight, not when you joined the check-in queue. So if you arrive twenty minutes before your check-in deadline and because we haven't got enough check-in desks open there's a half hour queue, then WE can stop you boarding because it's YOUR fault for not arriving early enough.
Will this help? I doubt it. The airlines need to take a strong stance against air-rage and stopping trouble makers before they board is an excellent idea. The almost impossible part is accurately predicting who will cause trouble before they've already gone too far, without banning the harmless ones who are just stressed out. Whilst 90% of air-rage offenders may have caused trouble at check-in, I doubt whether 1% of people who cause trouble at check-in turn into air-rage offenders. That makes it absolutely useless as a predictor of who you want to keep off your aircraft and just serves to increase the tension in the pressure cooker.