what Bell did is another experiment involving the correlation of different polarization of the lights at different angle. It is very difficult to see the direct relation of his experiment and the above mentioned fundamental differences in hidden variable theory and copenhagen interpretation. Again here politics takes over, complex formulas and experiments seems to be able to shut most of the people's mouth
It's not just theory; there is now hard evidence, too. Here is photographic proof, the first ever image of quantum entanglement (and violation of the Bell inequality), from the University of Glasgow last July.
paper: https://advances.sciencemag.org/content/5/7/eaaw2563
the experiment:
