"Being an advanced country, we would not have done so unless there were benefits in leaving"
This is the problem, the leave campaign sold leaving as a panacea to all sorts of different groups.
Many of these groups believe there are different benefits from leaving many of which are in direct conflict with each other.
Farmers want to be out of the CAP ( but still want to have the subsidies) but also want to have tariff free access to the single market.
Same with Fishing, we will get our waters back, and not have to follow and CFP quotas ( we will because these are actually internationally agreed) but still retain tariff free access to the single market to sell 75% of our fish to it.
At the same time, the Economists for Britain are proposing unilateral free trade with the world, ( calling it a world free trade deal although no such thing exists), whilst people in deindustrialised areas are hoping for more protectionism so that the industries return..
There are no good, well thought out reasons.
Even the Democracy and sovereignty point so often trotted out by the leave campaigners who don't want to get into these complicated issues are massively flawed.
The leave campaign objected to British judges rulling on British constitional law, and called them traitors.
They objected to Parliament having a say over when to declare article 50.
One of them has suggested a foreign power stop the UK sovereign parliament from doing what it thinks is best for the UK.
Another has suggested that the Queen close parliament so that Brexit can be forced through by the executive.
No, these were just buzzwords, to pay lip service to as were all of the other points of the campaign. A dark and nefarious group are steering this for their own ends and duping all the leave voters into asking for what will hurt them in then end.