If the missile is generating a lot of heat that heat is draining energy -- there is no free lunch.
Brian
I don't think anyone is saying that there is a free lunch... There are numerous varieties of missiles, and plenty of ways they travel. Many missiles flying at ground level have a motor which burns for a short period, leaving the vehicle to travel along a ballistic trajectory to target. Other missiles such as the BGM71 have much longer burns, and can flown to target with wired controls - so long as the motor produces more thrust than the weight of the vehicle it will fly (ie, thrust to weight ratio > 1).
Planes, gliders, and hypersonic gliders, have mechanical features which also generate lift. Most planes use wings to do this. Other aircraft, such HGVs, rely on the shape of the body to generate lift. HGVs rely on skipping on a boundary of thicker air, similar to how a stone may skip on water. The stone 'flies' along this boundary for quite some distance, skipping multiple times and rising into the air despite having no form of thrust. An analogy can be drawn to the mechanisms behind HGV flight.
You are correct when you say there is no free lunch. You are incorrect when you say hypersonic and glider are mutually exclusive terms.