Why should those working in the Public Sector get anything more than anyone else? Why not just get SS,etc.?

Why shouldn't Teachers,Cops,Firemen and others just pay into Social Security,and get a 401K or Roth IRA or whatever they want,just like the rest of the society.Why do Cops need rich pension and health plans that let them retire earlier than anyone else,for example.And exactly how do they think this fleecing of the taxpayers can be sustained.