What criteria allow rabbis to use the "Shomer Petayim" principle? [duplicate]

Question

There is a principle called shomer petayim (Meaning "G-d protects the simple". Based on Psalms 116:6.) which rabbis occasionally use to allow people to do something that would probably be considered dangerous. The rabbis make the activity permissible if it becomes evident that a significant populace is willing to take the risks.

For example, Rav Moshe Feinstein ztz"l used this principle to allow smoking despite the large evidence available explaining the dangers. See this article for details.

What criteria allows rabbis to use this principle to permit something? Can they freely use this for anything whatsoever that shows "societal normalcy" (i.e. society accepting the dangers?) For example, numerous people speed or weave on the highway. It's become the "norm" for people to exceed the speed limit by 10 - 20 MPH. There's sufficient evidence that increased speed causes increased as well as more severe crashes. But, since it has become societal norm, can rabbanim use this principle to allow people to do this? (I'm asking only about the halachic aspect of using this principle, here; not about prohibiting it b/c of Dina Demalchuta - i.e. one violates the law by exceeding the speed limit.)

The above is an example. I'm sure there are numerous others where this rule is applied.

Answer 1

Thanks to @Alex's source (Shu"t Tzitz Eliezer 15:39), this is what I also got from R' Schlesinger (an opponent of R' Moshe):

The שומר פתאים principle can only be applied when the danger is not known but speculated and to one that is not aware of it. So the advice to stay פתי implies that neither the Rabbi nor the questioner is aware of the danger.

Once the person IS aware of the danger he can not continue to pretend to be פתי and the principle would not apply. For instance, your example with speeding - no driver is unaware of the dangers of speeding - therefore this principle cannot apply.

But if a person tries a new drug which might be dangerous, but the statistics are yet to be known, or regarding smoking in the 60s-70s, when a person might doubt, he can be considered פתי and the principle applied.

You forgot to mention, that R"M's Psak was issued in the early 70s and that fits my answer perfectly!

If however only the Rabbi is aware of the real danger but hides it from the questioner, it seems to be לפני עוור and לא תעמוד על דם רעך.