1. a. Majority used for reaching LEO is used in atmosphere, yes, on account of drag -- which is a factor that will dramatically reduce the effectiveness of space elevators (a constant burn is required to maintain the anchor point's orbit). But pretend that's all irrelevant; an interstellar vehicle will *always* have more energy than any terrestrial unit. We're talking meteors against boulders here. 

b. History is littered with the corpses of men who thought a strategic advantage was 'negligible.'

c. There is no foreseeable zero-mass propulsion system rooted in real science. 

2. Smile again. You don't have any idea what you're talking about.