Regarding NASA and research suppression, I have an extremely difficult time understanding what could draw you to that conclusion. All manner of space based weaponry has been looked into by governments and found not terribly useful or practical. The energy you can bring along on a spacecraft is likewise very limited by mass constraints. The history of successes and failures in propulsion technology does not need a human cause; the universe itself may be to blame as may economic or practicality or political issues.

EDIT: a few figures to give some idea of scale. The Saturn V rocket carried a total chemical energy of ~2.5 kilotons of TNT full on the launchpad. A small subset of that winds up in the kinetic energy of motion. The Dawn probe can manage ~10 km/s by leaving its ion engine on for years on end and using electricity to shove fuel out the back extremely rapidly, producing a total kinetic energy change equivalent to ~14 tons of TNT (and not carrying the necessary energy in its fuel, merely using the sun to accelerate an inert gas electrically, and imparting much more kinetic energy to its fuel than to the spacecraft itself). Imagining a nuclear reactor driving a VASIMR or somesuch, if you used it up accelerating something for months you would create a projectile with a kinetic energy of impact a small fraction of that which you could get by using the core to make a nuclear bomb instead.