If you're going to shows, you probably should vaccinate for the 'flock killers', I posted on a thread a year ago a list recommended by Mr. Brown from First State Vet--and promptly got reammed.
I have seen at shows birds showing signs of Mareks, Lymphoid Leukosis , and many DQ'd for Coryza...
It think culling a bird that is 'sick' is a great practice. I've been using the ax more liberally and am very pleased with the results.
That does not meet my definition of breeding for resistance through--that's just good flock management.
In my book if you are breeding for resistance, you...