So, this is a philosophy that I try to adhere to. (And let me start by saying that I do so very, very imperfectly.) Let’s call it respect for non-human beings (for convenience, I’ll just use the term “animal” for this post).
The first and foremost tenet is that it’s wrong to kill an animal for my pleasure or convenience (including satisfying my taste buds, providing clothing or accessories or anything else for me).
The second tenet is that it’s equally wrong to inflict suffering on an animal for my pleasure or convenience. “Suffering”, in this philosophy, encompasses not only physical pain, but emotional pain, reduction in quality of life, etc. and also encompasses things like taking away habitat, which at a minimum creates stress, and is likely to cost life.
The third tenet is that, while killing in self defense (or in defense of another) is morally justified because I am defending myself against the aggression of another, killing to obtain limited resources is not likewise justified. (In human terms, this is the difference between killing someone who is attacking me with a knife and killing someone because the winter’s store of food is sufficient for one person but not two.)
The fourth tenet is that one should respect the autonomy of animals to the extent consistent with their health, safety and happiness. In the context of wild animals, this entails leaving them to live their lives with minimal/no interference from us. With respect to domesticated animals, it becomes more complex, because of the dependency we’ve bred into them and the responsibility that falls on humans because of that.
It really doesn’t matter whether I would do the killing/inflict the suffering myself or have someone else do it for me. (In other words, if I pay a contractor to build a house on a fox den, I’m just as responsible for the deaths of those foxes as if I had taken a gun and shot them.)
Now we get into a whole area that is rife with conflicting interests. I recognize that, by my very existence, I’m going to cost lives: the lives of animals living in fields that are tilled to produce my food and clothing, the lives of animals who are killed by my car and by the vehicles used to transport goods to me, etc. I can’t come up with an ethical argument as to why any of those lives should be valued less than mine. So, the line I’m drawing is an arbitrary one, and it is this:
I will try to live in a way that minimizes the amount of suffering and death my existence causes to non-human animals.
It’s not ethically justifiable in the context of those lives that are inevitably lost because of my mere existence, but it is very much more ethically justifiable than living one’s life in disregard of how many lives, how much suffering, is caused by one’s life and lifestyle.
As I said in the beginning, I do this very imperfectly. I use more resources than I need to, I indulge myself too much. I’m trying to be more cognizant of the unintended consequences of my choices.
I think there’s value in recognizing the limits of any philosophy. For one, it’s necessary in order to hone one’s thinking and one’s choices. For another, defensiveness just makes it appear that one’s position is weak. (Isn’t that what we tend to think of the defensiveness of omnis, and yet there’s plenty of defensiveness to be seen coming from veg*ns.)
So, I don’t have an ethical* problem with someone buying used items made from leather, wool or fur; IMO, that doesn’t increase the market for new leather, wool, fur, etc., and, to the extent that it decreases the production of a new item (even one not made from animal parts), it affects fewer animals still living. It’s not a choice I make for myself, because it hurts my heart too much to wear/use such items.
*Please note I did not say “vegan” – I said “ethical.” What I've set out is some of my thinking about my interactions with/ responsibilities toward animals. I'm not saying my philosophy is vegan. I do think, however, that the definition of veganism proposed by the Vegan Society sets out a broader ethical framework than the "don't eat, wear or use animal products" definition.