Still you will have to codify in some way what the "common good" is, because some way or another humans must be able to judge if something is against the common

Still you will have to codify in some way what the "common good" is, because some way or another humans must be able to judge if something is against the common good or not. I wonder how someone could possibly do that. The problem I see is that everyone will have his own idea about that. For some it will be upholding religious morals, for others it will be socialism. Could be really anything.