No, see, taking a risk is a potential harm. On a societal scale you add up the aggregate cost and benefit. On a personal scale you discount the harm you suffer by the risk rate, to arrive at the theoretical cost that you're weighing against the benefit. To go back to the car example, let's say you could buy a car with a low safety rating for $6000 and a car with a high safety rating for $8000; you weigh the risk-amortized costs of the lower-rated car being more dangerous if you get in an accident, vs the definite cost of the $2000 difference. And whether you take the risk or not is dependent on your personal decisions about your relative values.
So with circumcision specifically, the question is whether it's okay for parents to make that decision for their son. And as a society, if the risk-weighted benefits are worth less than the risk-weighted costs, then you can say on average it's a bad decision. Whether The State can take away people's right to make bad decisions for themselves is a really tough question, but taking away people's ability to hurt others via bad decisions is much clearer, it's the entire premise of "reckless endangerment." Going back to cars, it's not like driving drunk will definitely hurt someone, but it increases the risk so much it's a punishable offense.
So treating a "risk" as "zero cost" is socially irresponsible and thus, unethical.