Yes, you are exposed to radiation while flying -- significantly more than when passing through body scanners -- but it's not a risk with no benefit: you're flying. Body scanners, on the other hand, are a risk (I'll grant, a tiny one) with absolutely no reward as they do nothing to actually increase the security of flights.

We take risks every day and that's completely okay as long as the benefits make up for it. I'll take a 0.1% chance of dying for a million dollars, but I won't take it for a sandwich; I'll take a bit of radiation to fly, but not because of a half-assed security mechanism.