It appears to me that those preferring WTO/Hard Brexit over the Chequers deal don't understand the consequences of that.
WTO rules means you have to treat all WTO members you trade with equally. It you apply tariffs to one country/block, you must apply them to all. Similarly if you apply no tariffs for a given product to one country/block then you cannot apply tariffs for that product to any other WTO member. It's called the "Most favoured nation" rule.
The upshot is that you more or less have to impose a hard border both ways in Ireland to trade on WTO terms. The UK cannot import (for instance) Irish Beef into Northern Ireland "tariff free" unless it allows all other EU and WTO countries to export Beef into the UK (via whatever route) tariff free. So we'd have to be checking and controlling all imports across the Eire/NI boarder to claim WTO compliance. If we don't other, WTO Beef exporters (like the USA) will object.
Similarly, Eire cannot allow the UK or NI to export into Eire without checks. Eire will still be in the EU, and the EU is a customs union. The EU cannot allow unfettered access across the NI boarder and still claim WTO compliance. Since the EU does a lot of trade with the rest of the world on WTO terms, the EU won't want to risk aggro at the WTO.
The result of all this is that the Good Friday Agreement and WTO are basically incompatible with each other. You can have one or the other, but not both.