I think it's because they boil down to a belief system, and many people live and have values in a belief system. If one has a very high value of something, they live by it, or try to live by it, and think that every one should because in their reality it is of the up most importance. That's not to say that this is a good or bad thing. Personally, I hold say the environment as a very high importance. It's part of my spirituality and I believe that in order to succeed as a species, the environment should be strongly considered and we should be working on ways to help it. It comes into politics because politics dictates where our money goes. There is money in oil, there is money in timber and cotton, none of these things are environmentally friendly. There's money in renewable energy, but not as much. As a result, my spiritual belief comes into politics. I get amped up about it because I believe it is important for not only our survival, but for our childrens' children, should we get so far.
I think every one's beliefs should be respected and treated with care. They are what create an individual, and to tell some one that their beliefs or view is wrong is to tell a person that they are wrong in their core. I don't want to be told that my belief and values in the environment are wrong, just like some one else might not want to be told that their emphasis on family living is wrong. No one should be denied their right to be who they are. I think everyone can agree when I say no one wants to be told how to think. Unfortunately, not many people apply it to those that are not themselves.