Selling out to the EU?
The UK has been a member of the EU since 1973. Its entire economy is inextricably linked to the systems developed with the EU and to just jump off a cliff will wreck havoc. The vast majority of the UK's trade is with the EU. To self sanction this trade is "shooting oneself in the foot".
This is demonstrated by the deeply complicated matter of how to draw up an agreement to leave the Union. It has taken the better part of 3 years and there is still no significant or substantial way to leave, that everyone can agree upon.
It has devolved to a battle of ideologies, where one agreement is not agreed upon, only for that same agreement to be agreed on a few months later because their poster boy has put it forward. Ignoring the central fact that it conceded far beyond previously established "red lines".