So, the debate is on the motion:
This house would replace the NHS with a health system based on compulsory insurance.
(That is, rather than all healthcare in the UK being funded by general taxation and free at the point of use, as is currently the case, everyone would be obliged to take out a health insurance policy, run by the government and paid for by them according to their income.)
The opening speaker for the proposition is making a well evidenced and clearly argued case that the financial pressures on the NHS are such that the current funding model is unsustainable and must be replaced. Then the opening opposition speaker makes a point of information. When my grandma was in hospital, he says, she had her dinner on a paper plate that got thrown away afterwards. That's really wasteful. If they used china plates they could wash them up afterwards and reuse them and that would save money and the NHS would have enough money.
The proposition speaker replies that washing up lots of plates in a large hospital is really expensive too as you have to pay for the hot water and washing up liquid, not to mention the wages of the people who do the washing up. The opening opposition speaker picks up on this at the beginning of her speech. They could just put the plates in a dishwasher; that would take much less labour and would be much more energy efficient. The second proposition speaker replies to this point at the start of his speech. There would, she says, be a big capital outlay buying the dishwasher, and in any case dishwashers are less energy efficient than washing by hand. The second opposition speaker returns to the fray at the start of her speech by pointing out that hospitals already have machines for sterilising surgical instruments and these could be repurposed for washing dishes. The third proposition speaker shoots this point down by conjuring up a nightmarish vision of bits of uneaten spaghetti and tomato sauce ending up on scalpels.
And so on, and on, and on ...
What did they do there? They went down the rabbit hole, that's what. 'Going down the rabbit hole' is a metaphor, based on what happens when a fox is chasing a rabbit and makes the mistake of following it into its warren. As the rabbit knows its way round the warren and the fox doesn't, the fox ends up going round and round lots of twists and turns and ends up by losing the rabbit.
The rabbit is the point of clash in the debate. The fox is the debater. The rabbit hole is the argument about hospital crockery. In a debate on the motion above, a successful fox / debater will see that the point of clash is not what kind of crockery hospitals should use, but whether it is fairer and / or more effective for the state or the individual to take responsibility for paying for healthcare. She will not be tempted into a tortuous warren of dishwashers and Fairy Liquid which is dark and confusing and will take her away from the rabbit / point of clash.
How should the first proposition speaker have responded to the point of clash? Here's how. 'The NHS's financial crisis is too profound to be solved by focusing on small interventions to reduce waste, however worthwhile these may be. It can only be solved by radical reform. Compulsory insurance is that radical and necessary reform because ...' In other words, she should stay on the wide, bright field of key principles, and keep clear of the underground tangle of triviality.
Don't let the rabbit tempt you underground. Keep it in the light and (look away now if you have a pet bunny ...) go straight for its throat.