For instance, this oft repeated bromide has indicated to me a certain preference, or bias, to limit critique of secession from the EU, in general, only to purported UK gov't. interests in the "deal".

Best Alternative to No Agreement (BATNA

It is tempting to accept perversion of a (commercial) negotiation processes without examining, to begin with, agreement between the parties on its purpose. As the parties are agreed that UK withdrawal from treaties of the union is the instant purpose, what "deal" is disputed?

My understanding is, the "deal" is a euphemism for a collection of contracts between the parties which must be terminated in order to effect political and financial severance of any and all legal obligations addressed thereunder. Yet in review of the parties' records, I find scant evidence of parties' mutual dependence on those rules of socially acceptable and socially unacceptable conduct.

Which contractual obligations specifically, if any, do parties who represent some hundred millions of political constituents --and billions of "stakeholders"-- dispute?

Diversity is the key to economic and political evolution.