Isn’t most of the speed you spend on the first stage wasted on going up, though? And what little momentum you might get to keep when it’s time to turn into your

Isn’t most of the speed you spend on the first stage wasted on going up, though? And what little momentum you might get to keep when it’s time to turn into your orbit is also sucked away by air resistance. Rockets have to go directly up for the first part of the flight, and all that acceleration is wasted because what you really need is orbital velocity, which is going to end up being “sideways” relative to earth. An air breathing first stage would mean you have to give a little less of your fuel to going up, and you’re doing it in an environment with less air resistance.