The European Single market is a market for it's members only. It isolates itself from the whole of the rest of the world. If the EU single market was larger than the rest of the world's economies lumped together it would have some merit. As part of the EU the UK is not allowed to trade individually with the rest of the world. The UK is not allowed to trade individually with the largest part of the world's economy. As part of the EU the UK is isolated from the rest of the world.