The world is a different place
from what it was when we voted to enter the Common Market some 40 years ago. In that time there has been a huge increase in globalisation; inter-country trade with all parts of the world has gone through the roof.
So: do we need to be part of a low/zero tariff trading block as much as we did then ? The whole world is moving to low tariffs.
Take 4 minutes to learn a bit about Trade and Tariff History, see how international trade has gone through the roof in recent years, not all of those countries are members of the EU.
So: why should we suddenly do worse than other non EU countries ?