Put quite simply, it's ridiculous to have 600 men and women decide what's right and wrong. Excessive government causes more problems than it solves.
Yes, but we have those 600 men there to ensure that we don't have a society where six men decide what's right and wrong.
Why not have 60 million people decide what's right and wrong instead?
Maybe one day that will be possible, but at the moment, it's not, so we use representative democracy to approximate those 60 million people deciding what's right and wrong. It's hardly a perfect system, but it's better than all the rest.