What You Would Like To Do -v- What Can Actually Be Achieved
Firstly, this was a screw up. Can't be denied. We don't know who or why and to be honest even if we did it would add nothing to this debate (Ezy need to find out and ensure they reduce the risk of it happening again: note I say reduce the risk...to say ensure it never happens again, is fantasy - hopefully it won't but it sadly could..). The main thing is it did happen.
I have been in aviation for over 25years working in most departments, many UK and overseas airfields and have seen this happen (sadly) many times to many airlines at many bases (although not common) - so lets not get complacent and blame Ezy, it 'can' happen to almost any airline at almost any airfield. Ezy could have handled it better, but this is one of the hardest ops -v-customer service issues, especially if your resources are tight (crew hours, aircraft availability, airport closing times and weather issues).
It makes me smile to see all the posts on here about 'de-fuelling'. Now when I started in aviation, yes this would happen. Nowadays I know of no major airport in the UK where you can get de-fuelled, and I do not mean in theory I mean for it to actually happen. Fuel contamination issues and control measurers are so strong that 'practically' on the day for you to find a fuel company that has time (they serve multiple airlines) and the resource - potentially an extra bowser (capital costs of £100k+) that will be treated as 'contaminated' for many days after the event. it just does not happen - yep, in theory we know it 'can' happen and you may find fuel companies that say they will do it..you find me one that will do it on the day when they have so many other paying customers and their requirements to balance off. In the last 15 years I do no know of any UK (major) airport where you can get de-fuelled in such a situation. Not great, but that's the way it is!
Flying around empty - nice idea, but it ain't gonna happen. Apart from environmental issues, what about crew hours? That adds more sectors to their duty day, so get another crew..from where (wasn't this boxing day!) and all the time the night closure and weather at GVA are getting worse.
Best idea would have been (if possible) to swap the aircraft around and/or position this to another base (LTN/LPL) and send their aircraft to BHX...this is IF you have the aircraft and the crew, the crew have the hours and again the clock is ticking all the time.
So you are generally faced with the dilemma - canx the flight, as your logistical solutions are not practicable within the timescales and legal limitations you are faced with, and upset all the pax. Or off-load enough to make the plane able to operate.
This is a horrible situation and one I have sadly faced many times myself (due over-fuelling, last minute notification of broken seats, emergency door u/s etc - where you have more pax checked in than you can carry!
First choice, volunteers. If you are lucky and 'intelligent' enough as an airline to match your compensation to the specific problem and ensure the financial reward outweighs (if possible) the disruption and disappointment the customers will face - you may be lucky! - In my opinion the offer should have been the minimum require x at least 50% - this was a skiing trip/destination at Christmas (for goodness sake) not a quick Edinburgh and back where there are 'other' options available to the customers.
Sadly though if you do not get enough volunteers, you have to look and involuntary off-loads - never, ever a nice situation and sadly one I have been in more than once. I have never had to call the police/security but have had it in the back of my mind that it may have to come to that if my persuasion and negotiating skills do not work. In this situation (GVA skiing trip) the brave decision should have been made to offload more pax and protect the baggage of those travelling - in these days of triple A baggage security it would not take that long to find their bags (lots less than the 2 hours taken to force the passengers off - that the passenger posting on here related). To travel to a ski destination without your bags is pointless, you may as well not go. The decision to take all the bags off and limit the face-2-face confrontation was cowardly and dishonest.
Forget endangering the aircraft, simply if you have to offload these passengers against their will, then they are offloaded - their 'boarding card/documents are therefore revoked and they have no reason to remain in the restricted zone of an airfield. It is against the law to be in the restricted zone without the required permissions - if you are not on the flight, you have no permission to be there. A nasty approach to take, but that is your legal angle if you want it.
Someone said that you have a contract with the airline to fly to to GVA (or wherever) so they can't make you get off. Yes they can, check your contract. You will find that it agrees to transport you, it does not tie the airline down to when or how (you may have booked and have a flight number and times but this is not part of the contract). So therefore they can elect to not carry you today, on this airplane etc. Not saying this is morally correct or great - but that's the way it is.
Finally it always amazes me that people seem to think that aviation is the only industry that screws up. I (sadly) experience terrible customer service almost daily (and yes I do complain, but nearly always in writing to those that are accountable, not the poor sod that is there to face things on the day) this is in banks, supermarkets, the doctors, the hospital, on the roads - almost everywhere. Yet people seem to put up with going to hospital for your operation and being told that it is delayed/cancelled, being stuck in traffic jams for hours as lanes are coned off and no-one is working in them, filling your trolley full of groceries to find few or nil check-outs open..yet with aviation, such a complex logistical operation that is so (thank goodness) governed by multiple safety laws that we should always have a quick and easy solution and be able to rectify any situation.