I'll write slowly so you can follow this.
1. If we go to WTO rules we will need to apply tariffs to our exports and imports.
2. If we apply tariffs, then British manufacturers exporting will be more expensive.
4. If we decide NOT to apply tariffs, then WTO rules say that foreign importers can flood us with cheap tariff-free goods.
7. In other words, our wages etc reduced to same levels of 3rd world countries.
9. Now can you see why the hard-right of the Tory party are so keen on a no-deal Brexit?