This led to loss in sovereignty and freedom. Sadly though it doesn't seem like the UK politicians are taking advantage of this (regulatory, laws, borders, immigrations etc) just yet, but at least now it's possible.
My point is: How can you become a superpower again if your foot is chained to a sluggish red tape monster like the EU? Even Norway recently learned that the EEA is not fully respected by the EU (ferroalloy imports).
I think you - and seemingly most others, are focusing on the short term downsides and negative economic impact.
But that would have happened regardless. Now it's up to the UK to try to increase productivity again, and only then Brexit will make sense. As mentioned, this will take 15 years at minimum.