At a guess the risk assessment said the dangers are no worse than what is found in the normal pro cycling calendar.
Lets for example take the Passo Giau descent into Cortina d’Ampezzo (picked because i’ve done it and knew it made a good example). Included in the Giro on a very regular basis, no mass outcry about the dangers, and yet we find the following blind corner which is approached at very high speed.
https://www.google.co.uk/maps/@46.5223945,12.1194374,3a,75y,91.64h,67.47t/data=!3m6!1e1!3m4!1s-C5Ja0juAbdysb1vY5ovtg!2e0!7i13312!8i6656?hl=en
Which if you get it wrong leads to sheer rock face:
https://www.google.co.uk/maps/@46.5224628,12.1200604,3a,75y,73.88h,62.83t/data=!3m6!1e1!3m4!1s8q2a9jGXJicUPHkV9BpV-w!2e0!7i13312!8i6656!6m1!1e1?hl=en
And a wheel height wall ready to launch you into oblivion:
https://www.google.co.uk/maps/@46.5224995,12.1201379,3a,75y,68.57h,64.32t/data=!3m6!1e1!3m4!1suUgNhZsE1Y4eEabGvvvM-w!2e0!7i13312!8i6656?hl=en
If that section i’ve linked has been deemed suitable for racing umpteen times, then there’s no reason the Olympic RR course shouldn’t also have been deemed safe.
Its a case of the riders using their judgement about the level of risk they are willing to take. In the case of the Olympic RR, the riders will all have been out and recce’d the descent in the week leading up to the event, they all knew the risks, and they all made the decision they were worth it.