I assumed you guys knew how double slit experiments work specifically in regards to quantum entanglement when I made that statement. I realize now that this was very wrong for me to do.
So I'll explain some basics. What is a polarizer, it is basically a series of lines that breaks up light. Two slits is basically an extremely minimal polarizer. Now in reference to quantum entanglement specifically, photons are entangled through typically a crystal that divides each photon of light into two separate photons of different intensity, essentially a doubled image. The two images are then sent onto different courses and subjected to tests remotely to each other. The crystal in these experiments, or gas in some versions, acts as a polarizer. It inherently taints all results, because you can't know if the result you are reading is because of entanglement or because of the polarizing effect of the crystal on the light.
This is just one specific example of a loophole that has made every quantum entanglement experiment that has ever been devised inconclusive.