We did ok for hundreds of years before 1975, it is not a dark uncharted territory for us, that is just a shot to get the younger population scared
That's a little inaccurate since in those hundreds of years we were a ruling monarchy who quite often had to bow down to the power of France, Spain etc. Not exactly independent from Europe lol.
Our time of glory was because we were ahead of the curve industrially...we are not anymore. To be in a position to dictate completely on your own terms you either need the resources to be self sufficient, (we don't) or control those resources outside of your territories..(we no longer do). And arguably not even the likes of the US or China have managed it completely.
Alternatively you need to provide something essential to others. We don't have that either...despite the claims of the financial services..
Where I will agree the EU is bad for us is the emerging technology sector. The red tape and competing interests of the union nations, while handcuffed together, thwarts technological innovation as a business...RHC is right that they provide money for R&D but it then goes outside Europe post development to more accepting markets to actually make money. This should have been our new industrialisation but we chose the "gambling on crack" that is Finance.
Is this a reason to leave? It could be a very good one if we had built the business model to go past universities and have it ready to go when we exit...but we haven't which means we would be playing catchup from a standing start against the Yanks and Asia.
Exiting successfully required long term planning BEFORE getting to the referendum point. If you had a govt that had been in power for ten years or two parties agreeing to exit that had driven our economy to be at run when the decision was made then yes I believe we would have been better off out. If we had specialised industry that forced the remaining EU and other states to sign positive treaties with us then fine; out would be better.
Problem is, that force of will wasn't there and to leave then say "right what shall we do now?" Would be very very risky.
But as I said earlier...stay/remain...the EU in its present form is going to collapse. Will it be more costly being part of the process but leading the rebuild of a better replacement? or sitting on the sidelines feeling the impact of the collapse but with no control? I really don't know.