The argument that we will make up for (or made than make up for) the loss of EU trade with increased trade with nonEU nations has some serious weaknesses.Even if this is true it's still only about what is being lost through leaving the EU trade element
You also have to consider that we will also be free to setup new trade deals where we couldn't before, and look to new industries to excel in that may not have been so lucrative whilst still in the EU, all of which might work in our favour if effort is put into it
1. They are all much further away. Getting a Honda Civic to California takes a 2000mile plus boat trip plus a trans continental road/rail trip. This is against a train trip to Europe or a ferry ride across the channel. Time and time again studies have shown that (all other tings being equal) trade between parties is always more when they are closer. Just simple things like the time zones and ease of business meetings make a difference.
2. Non tariff barriers are more of an issue than tariffs. For example a chainsaw that meets UK standards (safety, emissions etc) can be sold in Germany, France etc with no extra paperwork. In order to sell in the US it may require a redesign for lower emissions, noise or different safety standards. At the very least it will require certification by a US body. The design and procedure may be different for India, China etc. The issue is that to reduce non tariff barriers requires "giving away sovereignty" which the Brexit campaign was extremely keen not to do. For example if a UK company feels it is unfairly being discriminated against by a French law (say UK beef is not allowed to be sold on "health" grounds) it can go to the ECJ as an impartial "referee". If the banking industry felt that an EU proposal unfairly discriminated against it, it could go to the ECJ and get a ruling. BTW those are not hypothetical cases, they actually happened and the ECJ ruled in the UK's favour. If the UK wanted to reduce regulatory barriers with the US or china, in the first instance it would almost certainly mean that the UK would have to accept the US or China's regulatory regime rather than the other way around, and secondly there would need to be an arbitration body similar to the ECJ, except almost certainly no where near as transparent or impartial. You remember the "secret courts" that the UK would be subject to if it stayed in the EU an inevitably accepted TTIP (which was a load of bull anyway). Those are most likely to be the arbitration bodies the UK would have to submit to in order to reduce non tariff barriers with countries like China or the US.
3. Market suitability, the US is an excellent market for the UK but other nations like china, india and "the commonwealth" are less suited. Simple things like a mismatch between the products we make and the ones they want. On the subject of "the commonwealth" (empire 2.0), much noise has been made about it's size, but the average GDP/person is $3000, in the UK it's around $30,000. If you take away the UK, Canada, Australia and NZ (who are responsible for over 50% of the GDP) it drops to around $1500. Who would you rather be selling too, 500million really rich people or 2billion poor people?
You are right, nobody knows, but if you see someone heading into the jungle with no map, no food or water, no experience and no plan you don't have to wait until they are found half dead in a week to know it probably won't end well.No one knows yet, it's very early days, and whilst everyone is trying to draw negative conclusions before anything has taken shape, all we have is this doom and gloom debate which is flimsy at best
Time will tell, but until steps have been taken we just don't know where it will end
It's done, the decision has been made, there is no point dwelling on what could of, should of, how about we start thinking about what positive steps could be made to strengthen our economy without an EU membership, there are plenty of other prosperous countries in the world that are not part of the EU membership