It appears increasingly obvious to me that what will make "hard Brexit" so damaging is the ill-will of the European Union. The EU is in a position to punitively harm the UK and most Europhiles on the Continent (who comprise most of those interested enough in the EU to run it) are going to use the opportunity for all it's worth. If Brexit supporters thought the UK would be better outside of Europe, the EU can ensure that's not true by setting incredible standards for exit.
Is Britain eventually going to find that a negotiated settlement won't work and they'll have to unilaterally declare their independence? When that happens, I promise to not snicker derisively. (But I will say, "SEE?!?!")