The polemical nature of the article is clear in the first paragraph, where you claim that “the best an ardent Brexiter like Liam Fox can promise is that we will survive Brexit”, which forgets to caveat that with Fox’s additional “without a free trade deal with the EU”, which is clear in the FT article referenced.
The main problem I have with this interesting piece though is the uncritical acceptance of Rousseau, where some of the tenets you quote are at best dubious- eg all people affected must have a say (where do you draw the line on that constituency?). Or how about the requirement that all people must be affected equally- how could that ever be true in a diverse society like the UK? I tend to agree with another correspondend who said it is difficult to see how the four conditions could be met “in a this world setting”.
It might have been more interesting to go at this the other way round- ie to what extent does the Brexit vote show the truth or otherwise of Rousseau’s conjectures?