Hah! Thanks for this tidbit, I had never stopped to think through their presence on the saturn 5, and absenece on other vehicles.
"It is in the area of crew safety that fins come in handy. In Saturn V the booster fins are not to provide perfect aerodynamic stability under all conditions - that would take fins of excessive size. But the fins reduce the aerodynamic instability enough to make sure that the astronauts can safely abort, no matter what technical trouble may afflict their space vehicle."
( https://books.google.de/books?id=MiYDAAAAMBAJ&pg=PA184 , continued from https://books.google.de/books?id=MiYDAAAAMBAJ&pg=PA68 )
Both could be true at once, just like when bicycle helmets are worn more as a fashion statement than out of confidence in their protective value. Or maybe he was just squelching rumors.
I say that because for the fins to do any good at all, boundary layer or not, the launch vehicle has to be moving at speed. I don't think a successful crew capsule abort would be likely past a couple of hundred miles per hour. If that.
That's not true at all. Every manned space launcher has provisions for bringing the crew down safely on a suborbital trajectory if orbit can't be reached. You would hardly give up on your astronauts just because, say, some stage failed to light. It's not like with an unmanned satellite, where it either gets to orbit or crashes/burns up.
Apollo certainly had provisions for crew abort all the way to orbit, which are discussed here: https://en.wikipedia.org/wiki/Apollo_abort_modes
It would have been worth a shot, just like jumping out of a speeding car about to go over a cliff. But you probably die anyway.