Nothing in this life matters. At the end of the day no one will give a shit who made more money. Why don't we just all be happy, and the only way to be happy, according to our western world view, is to have endless money. Fight the power, anarchy is the only way to go. Also, the earth is flat and the moon landing was fake.
If you are paid the same regardless of what position you are in, there is no motive to try to gain higher positions that take more work to achieve. For example doctors, who have to spend a lot more time and money in university than most other professions, would have no incentive to be doctors if they got paid the same as others who had to do less.
If this was the environment that we lived in, people would not be motivated to do more complex jobs, which require more schooling. Most people are lazy, and want to do the least work possible. There is a reason we need to have a pay scale, and why it is variable. People need a good work ethic, not hand outs...
I totally agree with VogonPoet, on what he said. If you give everyone the same pay then no one will have the incentive to work any harder and to increase in life. I don't get paid a lot at my work, but that is because I really don't work extremely hard and I don't mind not getting paid $30,000 annually, because I don't work hard enough to make $30,000 annually.