(Interestingly, they didn't do that with the Gemini spacecraft, since the launch vehicle--the Titan II--used room-temperature stable propellants. As such, the Gemini capsule relied on ejection seats to "punch out" during the earliest phases of launch.)
The escape towers on those early rockets were a function of getting the crew away from a low altitude fireball of an exploding rocket. It was even envisioned as being used while sitting on the pad. Nasa knew a suited and air supplied astronaut could reasonably parachute out.
They even had an extendable boom on the shuttle hatch for astronauts to be clip on, slide out the crew hatch, ride to the of the boom to safely clear the wing, then fall off the end.