Pneumonia is contagious, as evidenced by not one but a few of your birds getting it. Treating it may have saved those few animals but that doesn't keep them from getting it at all, nor getting it in the future...so it does come down to a management problem. Illness happens and everyone knows that, but animals that are prone to contract it and spread it to others don't have to be kept in the flock or the gene pool.But, Bee, even then, sometimes, things come up that may call for antibiotics. It is not just a management problem. Mine are quite healthy and managed well. I do not have contagious disease in my flocks, have not in all the years I've owned chickens, and if I did, I would not treat that nor do I advocate anyone else do so, either. But, crippling the livestock owner by taking away ALL our choices is not the way to go.
Building better immune systems and healthier stock can eliminate most illness, but medicating it doesn't do anything towards that goal. There are MANY farmers not using antibiotics on their farms or they will lose their organic status. They choose to cull immediately any animals that show illness, cutting their losses while building towards overall flock/herd health.
I haven't had a single illness in the past 40 yrs that "called for antibiotics". That's not a brag, there's a point to that statement...if you determine you will use ATBs as a solution to a problem, then it calls for it. If you determine you will use more sustainable methods to solve that problem, then it doesn't call for them.
ALL their choices are not removed when the ATBs are removed, just the ones they favor most. There are many choices still left to manage livestock and keep them healthy without using oral or IM/IV ATBs. Yes, animals will die and that's okay...in that manner the weak are removed, the strong are left behind to make more strong animals. Wild chicken flocks, wild cattle, wild horses are all thriving and reproducing without the benefit of ATBs. Judicious culling of one's own flock can produce a flock that is much like the wild ones...stronger, healthier and more sustainable for the future. And not just through culling, but in overall conditions in which they live, one can influence the overall health of the environment wherein they live, encouraging healthier soils, healthier diets, healthier air in the coops, etc. It's a varied and ongoing approach to a single problem...flock health.