If you want to well and truly win an argument, defeat your opponents strongest argument, not their weakest.
That's not what the dyed-in-the-wool brexiters want. They want to revert back to WTO rules, then unilaterally remove all import tariffs.
https://www.express.co.uk/news/poli...-trade-free-market-institute-economic-affairs
https://www.cgdev.org/blog/beyond-brexit-unilateral-tariff-reduction-really-such-crazy-idea
https://www.ft.com/content/2a009b7c-2d71-11e6-bf8d-26294ad519fc
https://policyexchange.org.uk/brita...-tariffs-and-become-a-champion-of-free-trade/
https://blogs.sussex.ac.uk/uktpo/2018/02/22/will-unilateral-free-trade-be-the-making-of-brexit/
https://www.bbc.co.uk/news/business-40972776
These unilateral-free-tradeists are fanatics. Brexit is only a small part of their revolution. They want to scrap all import duties and make Britain a modern day Singapore. They have zero interest in arguments about immigration... they'd actually probably be pro-immigration although they wont admit it.
But the only thing they really care about is scrapping import duties. Chinese steel would be dirt cheap, clothes from India would cost only pennies, electronics from Asia would be much cheaper. They argue that services make up the vast majority of the UK economy, and services would benefit from cheap world wide goods.
Of course they are ridiculous fanatics. Our manufacturing sector would collapse unless others agreed to also drop their import tariffs. We'd have no rights to sell our services into Europe or America or anywhere else.
But it's the fantasy they've been dreaming of for decades. They have no interest in trade deals. They want revolution.