When you raise animals commercially, who's to say what's okay when it comes to deciding what to sell and what to discard after they're slaughtered? The market is basically the final arbiter of whether your business is allowed to continue or not, right? If you're not making money, you're losing money, and I think you'd probably go broke if you only sold the feathers. It costs money to raise chickens, and feathers aren't worth much compared to the meat, so according to the market it would not be okay to raise chickens just for their feathers, you'd need to sell the meat too.
Hmm. That's a solid - and totally expected - defense for the marketers. Now, defend the marketers of rhino horns and elephant tusks.
If people were raising rhinos and elephants commercially to satisfy the demand for ivory and rhino horns it would be a fair comparison (there would also be a lot more of them), but poaching wild animals is a crime. There are many illegal things people do to make money, I'm not going to defend them.
Let me be blunt, then. This post wasn't about chickens. It was about slaughtering animals for their skins. Is this really necessary?
I guess it depends. Most of the skins used in our society come from cattle, so as long as people eat beef, there will be a steady supply of leather and it would be wasteful not to use it.
Of course you're talking about furs, and in general I agree that it's a bad excuse to raise animals. Fur bearing animals aren't well adapted to being farmed, since they are quite intelligent and solitary. It seems cruel and unnecessary for them to live and die that way for such a frivolous purpose.
On the other hand, trapping is one of the few forms of income for natives in remote areas of Canada, and with the push to ban fur they've been largely stripped of that income which had enabled them to live a somewhat independent and traditional life. This is a contributing factor to the pervasive sense of hopelessness many natives in remote villages feel, leading to substance abuse and suicide.