Urgh stands happy besides a big circular object made of rock, with a chisel and hammer (primitive, of course) nearby. His friend Arh approaches presently.
Urgh: Look what Urgh did!
Arh: What be?
Urgh: Me invent rolling object! You push, it roll around.
Arh: What for?
Urgh: *shrugs* It be used to transport things maybe, put object in middle and push.
Arh: Urgh not serious!
Urgh: What?
Arh: Urgh rolling thing untested. What if rolling thing rolls over someone asleep? Urgh kill people with rolling thing!
Urgh: Well, Urgh not planning to use around people...
Arh: But can you prove it never happen?
Urgh: Um... no...
Arh: Therefore rolling thing dangerous! Not use!
Urgh: So, because me cannot prove not dangerous, you say dangerous?
Arh: Yes!
Urgh: Arh realize using logical fallacy right? Argument from Ignorance. Arh cannot say something dangerous just because no proof it is not.
Arh: SHUT UP CAPITALIST SWINE! LOGIC NOT INVENTED YET!
Urgh: Um, capitalism not invented yet either.
Arh: SHUT UP OR ME SMASH URGH WITH ROCK! Also, Urgh not made environmental impact study of effect of rock on grass.
Urgh: Well, rolling thing more useful than impact of rock on grass... tradeoff seems pretty good for us...
Arh: Tradeoff? No risk is acceptable! Rolling thing might lead to vegetation death, killing animals, no more food, we all die!
Urgh: But Arh not know that for certain.
Arh: BUT IT POSSIBLE! Therefore Arh assume until you prove otherwise!
Urgh: ... Arh using Argument from Ignorance again...
Arh: LOGIC NOT INVENTED YET!
Urgh: ... and why burden of proof on Urgh? Why not think Arh's method preventing progress and thus putting more lives at risk than the alternative?
Arh: BECAUSE YOU CAPITALIST SWINE! URGH WANT TO MAKE MONEY OFF ROLLING THINGS AGAINST HEALTH OF TRIBE! ARH HATE YOU!
Urgh: ... but money not invented yet.
Arh: SHUT UP URGH!
This was the first ever recorded use of the Precautionary Principle, the liberal's dream of pseudo-scientific, illogical security. In the year 2007 CE, we are still living in caves and scared of rolling things. Hooray for the Precautionary Principle!