I think the answer lies in the word "acceptable". If the risk does materialise and you can still look at yourself in the mirror and say "it was worth it", then it is acceptable. It's to do with where you hold the balance of the risk against the related rewards, and that can be different for different people.

So Rabbi-Sol finds the risks of flying unacceptable. But others do not. No point in arguing it out, because for him the rewards (getting there faster, the thrill of flying, the pleasure of queueing to be body-searched etc) are too light in his balance against the risk of an accident, loss of life etc.

It is also to do with how much you value the things to be risked. Your life, for example. If you think a longer life is your ultimate treasure, you will not risk it for anything.

Risk is fear-related.