It’s implied.

> I drink diet sodas. I have received many emails/calls/texts from friends and family telling me about the "news" of them being a possible carcinogen. To every such person I say: Alcohol is a KNOWN carcinogen. Drinking alcohol causes cancer. So don't lecture me about drinking diet coke until you have given up on beer

The poster compares the risk of aspartame being a « possible carcinogen » to Alcohol, which is a « KNOWN carcinogen », specifically comparing the different classifications.

But relative risk is irrelevant. They still don't somehow cancel out. My aspartame consumption poses some risk to me, and that risk doesn't depend on the habits of the person telling me about the risks of aspartame.

That’s not the point, there’s no claim it cancels out. The point is about the risk tolerance. We all take risks in our life, and the risks posed by aspartame are lower than that of alcohol.