^ When you say its not workable, you mean it could lead to economic head wimds, not that it cannot work or is not feasible.
The problem is tying the UK to a set of policy and regulations which the EU control and that influence other non-EU economic associations the UK is looking to negotiate is just as harmful to the UKs future world wide trading relationships, one where it clearly sees a diminishing EU role.
The problem remainers have is that the EU has loomed so large in their vision for 4 decades they become unable to see anything else, the else is a big world.