Such a drive would use a hypothetical form of thrust that does not require any outside force or net momentum exchange to produce linear motion, and therefore necessarily violates the conservation of momentum, a fundamental principle of all current understandings of physics.
Such a drive would use a hypothetical form of thrust. This hypothetical form of thrust does not require any outside force or net momentum exchange. This is to produce linear motion. This hypothetical form of thrust necessarily violates the conservation of momentum. Momentum is a fundamental principle of all current understandings of physics.