There are lots of known carcinogens for which the dosage is important. For example... sunlight.

There's a reason the "this product contains a chemical known to the State of California to cause cancer" warning labels are a bit of a joke, after all.

benzene is not one of those

One molecule of benzene will guarantee a cancer case?

You aren't guaranteed to die from being shot in the head either. However there are things which the medical community recognizes have no safe level of exposure.

From the original article: "The toxicity of benzene in humans has been well established for over 120 years. The hematotoxicity of benzene has been described as early as 1897. A study from 1939 on benzene stated that “exposure over a long period of time to any concentration of benzene greater than zero is not safe,” which is a comment reiterated in a 2010 review of benzene research specifically stating “There is probably no safe level of exposure to benzene, and all exposures constitute some risk in a linear, if not supralinear, and additive fashion.”

Yeah and you literally can’t breathe without risking being exposed to benzene. It’s in many adhesives, paints and petrol.

If you want to adopt a zero tolerance policy for benzene then you’d need to ban petrol. Or stop breathing.

I'm certainly not going to rub petrol on my skin.

It just takes one UV ray hit one strand of dna and lead to cancer.

The links are about talcum powder, not sunscreen. Totally separate type of product that has nothing to do with benzene.