I feel that people will always have a difficult time in defining the value of a life and what kind of lives we should defend because of differing worldviews. When you look back to history, we’ve even been through times when we didn’t value every human as an equal- for example when there was still black and white segregation in the US. We as humans seem to like to differentiate things, not simply view and value something as simply being another life contributing to the world (no matter how big or small the contribution). To answer the question, I think our inability to define a common value because of all these differentiations is directly playing a role in forming an animal rights ethic.
Optimally, we would define the importance of an animal’s life by simply having consciousness and being a life. I feel that, in valuing something simply for it’s existence, we allow ourselves to truly live by the Golden Rule. In other words, by living in a manner where we are treating every conscious thing the way we would want to be treated, everything is fair game. This may or may not change the way animals are seen and treated, but I feel like if we can value some animals as our pets and family, why can this not be extended to other animals, and then nature in itself?
Lastly, the way I like to look at things is that if I don’t take care of and maintain things in my house, the house is going to be non-functioning and awful. Earth is our only true home, and if we abuse it and don’t take responsibility for our actions, it’s going to backfire and stop functioning in the same way. I feel that if everyone took this idea into mind, it would naturally change how we value things, animals included.