Agreed on just letting nature run its course. Survival of the fittest, natural selection and all that jazz makes a lot more sense to me than "wipe out the ill, bleach your entire property, then start over again with delicate, immuno-compromised birds and practice strict bio-security!"
As for selling the ones I'm not keeping, I'll advertise them as disease-resistant, cocci-immune and free-range raised. Or something like that. Out here, unless you're buying the vaccinated birds from a breeder, your buying a bird that's got SOMETHING. (Trust me, I know!) I'll just tell people they've already been sick so they should be good to go

Of course, for those adding to existing flocks, I'll just let them know that if their birds haven't been sick yet then maybe they might not want mine unless kept separately.