I moved my reply to the Brexit thread. Hope you don't mind.
This analogy doesn't make much sense to me. Brexit is supposed to be a negotiation between the UK and the EU. Failing to prepare for all the potential outcomes of the negotiation is irresponsible, and gives the EU massive leverage as the UK will need to avoid at all costs the outcome it hasn't prepared for.
(Please remember that while I think the UK is harming itself in leaving the EU, I think the EU will be better off with the UK out and in a close relationship, so I would really prefer that Brexit went through.)
It's true that in general, all outcomes should be prepared for. As such, Cameron was an irresponsible fool not to prepare for Brexit winning marginally – or even by a landslide – in the referendum.
However, there is always a context. In this case, there is a fully viable fallback option: cancelling Brexit*. Granted, this would be far less than politically ideal for certain people, but the UK's current political situation within the EU isn't really bad, all things considered. Especially when considered against the situation of a no-deal. If the UK Parliament is unable to agree on what they want, and thus being unable to negotiate with the EU – or even just make a consistent, non-ridiculous statement of what the want, then wouldn't the prudent thing be to cancel Brexit*, calm down, and first agree on what they want?
Actually "preparing" for no-deal is hard. As
@uppi points out, there are quite a few effects that will result from a no-deal Brexit. Just considering what the UK needs to import to keep functioning, is staggering. And many of those things
can't be stockpiled, because they expire! In the case of a no-deal, the top five imports to prioritize are, officially, as follows:
1. Life-saving drugs
2. Medical devices
3. Fresh food
4. Nuclear power plant parts
5. Chemicals to purify drinking water
Notice that: Clean drinking water is
priority five!
There's absolutely no guarantee that any of those will be easy to keep importing. Even half a day's extra delay could make some drugs and medical devices useless, so all trucks carrying those must somehow be identified and given priority through customs.
Is it really responsible to expose people to these kinds of risks just because the UK Cabinet, the UK Parliament, and the EU can't agree on a deal, or would it be more responsible to cancel Brexit*, and later find a way through it? And if no-deal isn't as responsible as revoking, why spend this much resources on a less responsible fallback option?
* (Yes, revoking A50 is only valid if it is sincere, but realistically I don't think anyone will feel like stressing that point if the alternative is a sudden no-deal situation.)
It seems to me the only way that the UK could rule out no-deal Brexit, for real, is to give the EU whatever it wants to ensure that a deal is made...but no one has seemed willing to say that out loud.
This looks like you've been listening too much to Brexiters, if I may say so. Do you really find the positions of the EU to be unreasonable?
Making sure the UK covers pensions and such for British EU civil servants, protecting the rights of people who will end up on the wrong side of the borders, protecting the internal market of the EU, and maintaining the Good Friday Agreement seems like very sensible positions to me. During negotiations the EU even accepted the British demand that all of the UK should be included in the backstop.
The very easiest way to guarantee Brexit would be for the current UK government to accept that only Northern Ireland is in the backstop and get enough Labour MPs to vote for that. They'd lose the DUP support, but after a-deal Brexit, could hold new elections claiming that they delivered Brexit, and probably take back many (most?) of the voters that have run of to the Brexit party. Labour could probably do the same with LibDem voters.
But if they can't agree on a Brexit they want, the responsible thing would be to revoke instead of going for no-deal.