“Can’t they just slow down with a rocket before hitting the atmosphere?” or “Why can’t they glide gently through the upper atmosphere losing speed gradually?”
In fact, NASA’s original conceptual studies for the Space Shuttle envisioned a smaller space plane with lower wing loading which would have experienced less severe heating during re-entry and may not have required fragile and high-maintenance ceramic tiles to protect the airframe during re-entry. The final design was driven by Air Force requirements for sufficient cross-range to permit landing near the launch site after one orbit and payload capacity sufficient to orbit large spy satellites. This, in turn, dictated a size and wing loading that made re-entry challenging.
Still, one way or another, you have to dissipate all of that energy imparted by burning fuel on the way up, and by far the cheapest and lowest mass way to do it is letting the atmosphere do the work and dissipating the heat with an ablative heat shield.
I wish I’d gotten Truax’s details on his "rotisserie " approach to reentry. The video linked talks about the aluminum but not steel nor about the CMB’s cryogenic black body of space into which the rotisserie radiates.
The tank presents a relatively blunt (cylinder) surface for more-uniform heat load. Having an extra 200C (assuming the space-side of the rotisserie is about -200C – or ~70Kelvin on average) for the Stefan-Boltzmann fourth power law is a non-trivial advantage.
PS: Although I expect the video’s arguments might be adequate to eliminate the “skipping stone” approach to repeated bleed, it didn’t make the case in adequate detail for my casual investigations.
Even assuming Starship’s areal mass is far lower than the figure I used, Truax couldn’t have been that far off so I must have misunderstood what he was talking about. Maybe he was just talking about the booster return which would have been suborbital velocity.