In Apollo 11 Flight Journal the following is stated:
The crew will make re-entry without suits or helmets on. Although this was a controversial decision on the first Apollo flight, Apollo 7, when the crew wore suits but no helmets contrary to MCC's advice, by now it is regarded as routine.
According to wikipedia, during Apollo 7
They perceived a risk that their eardrums might burst due to the sinus pressure from their colds, and they wanted to be able to pinch their noses and blow to equalize the pressure as it increased during reentry.
From Apollo 7 Flight Journal:
258:23:57 Slayton: Okay. But the mode we wanted was to have them on without being latched down to the neckring. [Pause]
258:24:04 Schirra: Deke, I can't get my hand in there, besides a handkerchief, and we're not at all safely braced for landing. We'll evaluate as carefully as we can. [Pause]
258:24:17 Slayton: Okay. I think you ought to clearly understand there is absolutely no experience at all with landing without the helmet on.
258:24:24 Schirra: And there is no experience with the helmet either on that one.
258:24:27 Slayton: That one we've got a lot of experience with, yes.
258:24:30 Schirra: If we had an open visor, I might go along with that. [Pause]
258:24:35 Slayton: Okay. I guess you better be prepared to discuss in some detail when we land why we haven't got them on. I think you're too late now to do much about it.
258:24:43 Schirra: That's affirmative. I don't think anybody down there has worn the helmets as much as we have.
258:24:50 Slayton: Yes.
258:24:51 Schirra: We tried them on this morning.
258:24:53 Slayton: Understand that. The only thing we're concerned about is the landing. We couldn't care less about the reentry. But it's your neck, and I hope you don't break it."
Was there any kind of official report with risk assessment to implement easing off of the rules and allowing reentry without being pressure suited? Did they consider Soyuz-11 scenario (which happened later in June 1971)?