An agreement to share a market also requires agreement about who makes its rules. That doesn't make economic integration a mistake. It means the political obligations are part of the offer and should be discussed openly.
The German Zollverein provides an interesting historical example. The customs union established in the 1830s reduced barriers between participating states while they retained separate governments. Prussia's influence within it also made the arrangement politically significant, particularly in relation to Austria.
Common trade needs common decisions
Removing internal barriers creates questions about the external tariff, administration and disputes. Those decisions affect the participants even where they haven't created one government to make every other decision.
The Zollparlament, elected in 1868, gave the customs arrangements a parliamentary institution before German unification in 1871. The sequence is revealing. It doesn't prove that the market inevitably created the empire. Wars, diplomacy and the actions of governments mattered enormously, and some participants resisted Prussian political ambitions.
History is less useful when it is reduced to a conveyor belt towards a predetermined outcome.
Explain the bargain in full
The modern European single market is a different institution. Britain can reasonably debate arrangements for closer participation without assuming that nineteenth-century Germany supplies the answer.
But the question about rules remains. Which obligations would Britain accept? What influence would it have over changes? How would disagreements be resolved? Which choices would remain national, and which would be constrained by the agreement?
Closer economic ties may offer benefits worth those constraints. Distance has costs too. Neither side should have to pretend that the choice is between commerce without politics and sovereignty without consequences.
I want the arrangement described as it would actually work. People can then decide whether the access and cooperation are worth the obligations, rather than being promised a market whose shared rules somehow won't require shared authority.