Re: ex muslims
There are examples when munafiqeen (the people who were hiding that they were not actually muslims but acted like muslims..and did not cause other harm), despite it was known by muslims, no punishment was given to those people.
Murtids were those who kept changing their position..and had intent of causing harm to muslims by going back and forth in to opponent camps. These people were punished harshly.
Judging someone if that person is actually has intent to cause harm is difficult and punishing these people is also very difficult and sentence must not be given to anyone just because that person is no longer practicing muslim...or mentioning doubt about the faith.
In other words, just changing the faith and not causing damage is OK in my humble opinion.
Other logic:
We all know, openly admitting is different than keeping it to self.
A confessed criminal is treated differently than the one who does not.