It's true enough that something that can't be proven requires no disproof, but science doesn't deal in proof. It deals in evidence, and at present, the preponderance of evidence supports the BB theory. That doesn't prove beyond any doubt that it's correct, of course, but it'll remain our go to explanation until and unless new evidence points us toward a better one. Membrane theory offers some interesting possibilities along those lines, but so far the new theory isn't quite robust enough to supplant the old one.