//There are a large number of people on this site who still believe that Brexit is a good idea – I want to disavow them of that belief.//
Then, in my case, you’re in for a long haul.
As usual, I’ll say it again: the principle aim of Brexit was to ensure that the UK ceased to be a member of the EU. Job done. The rest is noise.
As far as rejoining goes, there is not a credible party which has any intention of doing that - especially as the terms will be even worse than those of our previous membership (if you could imagine such a thing). In fact, it is far more likely that the EU will have collapsed long before any campaign of that nature succeeds.
What you really need to do is to ask yourself this: if the EU is such a wonderful institution and a resounding success, why is it that no group of countries anywhere else has seen fit to form something like it? I'll leave aside the former Soviet Union for obvious reasons, but if you want to include it in your argument, feel free. You would think that countries would be queuing up to form fiscal and political unions where their laws are subservient to those of the Union and their Parliaments are effectively neutered as a condition of membership. After all, the EU has been in existence in some form or another for over sixty years and there has been plenty of time for other nations to "see how it goes". But strangely, none seem to be doing too bothered.