1)  We live in a country where there is separation of Church and State.  It is this separation that allowed the Catholic Church to grow and flourish when it was very much a minority religion.  It seems grossly unjust to decide that Catholics no longer want the separation, once they have been able to grow big enough to bully others.
2)  Evangelizing and forcing others to adhere to Catholic doctrine are two different things.   If Catholics were so successful in evangelization that everyone in this country became Catholic -- that would be one thing. But we are nowhere close.  The Catholic Church is actually losing faithful, so I don't see this happening soon.  .  
3) The Catholic Church supports freedom of religion and agrees that there is more than one way to God.  So, why would Catholics want to impose their beliefs on others?