We don't generally accept a theory as mainstream until the internal problems are consistent. I was just reading about Quantum Electrodynamics and there were a bunch of problems with infinities, like when certain quantum mechanical principles of the electron worked out by Dirac were applied to entire atoms, it gave nonsensical answers like the atom has infinite energy. Once a theory came along that got rid of these problems, it was accepted, especially since it was in accordance with experimental observations.