You have Juncker backwards. He was saying internal EU borders are a bad idea.

Rejecting all borders is a tenable ethical claim - indeed it's hard to justify why states should exist in most ethical frameworks that value human equality - but Juncker didn't go there.

But yes, Britain sabotaged the EU, including its having a joined-up defense and border strategy. Indeed, you might expect the departure of the most Eurosceptic nation to strengthen the EU.

You didn't read his comment. His statement was unequivocal and didn't talk about EU internal borders specifically: it was a statement of principle.

But hey, if you want to believe these people think differently to how they actually do, go ahead and believe that.