That depends on quite a few factors. One of the first questions to ask, is why is it so rare? Is it a heritage breed that fell out of popularity? Is it a newer breed, that has not gained popularity? Is it because chicks are hard to hatch from them, thereby, making it more difficult to maintain the line?
Next, you need to take a hard look at your existing stock, and see what it would take to bring the line up to where it needs to be. Even with lesser quality stock, a line can be brought up, but it takes time, and lots of culling. Are you willing to hatch out the numbers required, and cull the ones that don't meet the standard?
With each generation, when done correctly, the line should improve. In addition, with each generation, you are further removed from "inbreeding", and eventually you are not even line breeding, so eventually you will have enough genetic diversity. That shouldn't be a big problem. It's more about time, effort, record keeping, hatching numbers, and culling.
If you are starting out with really good quality stock, and you like the breed, eventually you will need to hatch, and cull, just to maintain your own line anyway. There are a lot less biosecurity risks involved when you are dealing strictly with your own stock, and not introducing new stock to your property, and flock.
The only moral obligation is to ensuring you have a well cared for, healthy flock. If you feel that breeding might be overwhelming, and the overall well being of your flock would suffer, then don't do it. If you feel you might be able to accomplish a breeding program, while enjoying it, as well as maintaining the well being, and health of your flock, then go for it.
Your replies have helped.
