Air-breathing hypersonic engines

Al Globus wrote,

"
The point is that using a scramjet to eliminating the enormous amount
of oxydizer required for a rocket eliminates all kinds of complexity
and problems, some of which are not at all obvious.
"

I'll grant you that. But we have 50+ years of experience with those
complexities, and we understand them quite well. Hypersonic propulsion
introduces a whole new set of complexities --- for example, management of
atmospheric heating of the airframe during extended high velocity flight
within the atmosphere --- with which we have very little experience. Do
you prefer the devil whom you don't know to the devil whom you do know?

Ron
******