Ah, SSTO yet again. I always cringe at these Holy Grail projects, ssto, supersonic airliners, over-elaborate vaccum cleaners etc.
The simple arithmetic of rocket science says everything you throw away is advantageous. Carry no surplus baggage. Works well in planetary life, works even better in space. You need to minimise the amount you bring back to earth and you maximise payload by dumping as much as you can on the way up. Perhaps breathe a little air at low altitude, but dump the air-breathing bits before they become dead mass.
Manufacturing cost is minimised because the bits you throw away can be produced in greater volumes and become vanishingly cheap. It's what the Russians do, it's what the Chinese do. We would be fools not to copy the world's leading nations.