Hydrogen/Oxygen fuel systems for rockets
I was under the impression Hydrogen-Oxygen rockets were extremely inefficient for propulsion. The amount of time you could 'burn' the engine would be too short to make meaningful speed out of it (IE., conventional wisdom has it that you'd 'burn' the engine halfway to your destination to accelerate the entire time, rotate and 'burn' to slow down, or find some other means of slowing down - but a Hydrogen ship could not carry enough fuel to keep burning halfway to even a moderately distant destination).
And, yes, I am aware the "pollutants" break down over time, and we WOULD have forever [8>], but the message the society always put forth is that no pollution would ever take place.
electromagnetic propulsion systems
Ummm...unless I am horribly mis-informed, electromagnetic fields are a product of concentrations of metals in a gravity field. Planets, that is. Once you are outside of a planetary gravity field, the background EM fields of space are chaotic, random, and minimal. FAR too little to use as propulsion.
In any case, you'd need to make the ships out of metal (and TONS of it - it takes feet upon feet of metals to provide sufficient shielding against the hard radiation of deep space). I am not aware of any refining or forging processes that do not damage the environment. And, a fleet of ships big enough to move the population of Earth?
A fanatic is one who, upon losing sight of his goals, redoubles his efforts.
--George Santayana