It's because I believe that terms such as "quality of life" and "making life better" are objectively meaningful that I find objective morality unavoidable. If one considers "quality of life" an arbitrary measure, such that one can define it to be, say, winning a certain number of Olympic medals, then one can follow measures directed to that outcome, and have an East German-style society. However, I don't accept that "quality of life" is as mutable as that.
I'm not quite sure how most of that follows from my post, but ok.
Anyway, if I'm right, then you're essentially saying "quality of life" is an objectively definable term, and same for all humans. I certainly don't agree with that. If I consider winning Olympic medals the most important goal in my life, then it bloody well is a defining factor of
my quality of life. Quality of life means very different things to different people, and that's the way it will always be. The reason we can make social contracts such as laws and moral systems is there are several things practically every human desires, such as safety, food, shelter, health care et cetera. Whatever falls outside those basic needs is not always provided by social contracts, but is still an important factor contributing to quality of life.
Your example about an "East-Germany style society" doesn't really work against my opinion anyway; rather, it's an argument against yours. My idea is that everyone decides what defines their own quality of life, and make social contracts in order to ensure those conditions are satisfied. Your example was of a government deciding for everybody what "quality of life" means. In this case, it meant "a certain number of Olympic medals", which obviously is not to the liking of most people. However, the idea is not ideologically different from imposing any other set of values on others.
When you say you can objectively define what "quality of life" means for all people, you are doing precisely the same thing as the government trying to make everyone into athletes: imposing your values on others, claiming they are better or more "objective" than theirs.