The worst is that it's an entirely self-inflicted wound. If Cameron hadn't enabled a referendum, the UK would have likely carried on the same, just with discussions inside the EU about immigration.
I feel like that's both true and not true.
Cameron, being an almighty idiot, of a kind only the most elite educational establishments can produce, not only gave us an unnecessary referendum, but chose the worst possible moment to have it. Like, 5 years earlier or 5 years later it probably would have gone the other way and we'd all have carried on.
It's a bit like the argument about guns and suicide. If people have a referendum lying around their house when they are going through a crisis, they might make a impulsive decision with irreversible effects. I'm sure statistics show that's far more likely than a referendum being used to deter an intruder.
But just as someone who kills themselves might have a very long-standing mental health problem, the Brexit vote did stem from very long-standing and deeply-rooted problems. Brexit has always been latent in the UK. And its relationship with the Continent has always been difficult, afflicted with contradictory needs and desires.
And the Tory party especially has always been divided over the issue, it's long been their biggest single internal problem, that they periodically wreck themselves over.
Also, to declare it to be 'self-inflicted' kind-of assumes there is a single British 'self' to make a conscious decision. I don't think that's true. It's surely more a a result of long-existing contrary forces in British society interacting. This disaster was always latently present in the UK, going back to the end of Empire.
Actually I'm not even sure it's true with an individual person engaging in self-harm, yet alone an entire nation. People are composed of warring forces as well.