According to this study, the main reason people have left is that they no longer believe in what their church teaches, whether protestant or Catholic.  This loss of belief is often ignored by Catholics, as people cite the scandal, the hot-button doctrines of the day, the liturgy and several other things, contributing factors but not the fundamental one.  

There is a difference between losing belief in a  institution and losing belief in God. That distinction is often lost in these discussions. The study shows that the majority of "nones"  believe in God, many pray.  

It is doubtful that having someone wish them Happy Holidays instead of Merry Christmas caused anyone to lose their belief in the doctrines of Christianity. Also, I am unaware of laws that forbids people from mentioning God in public. God is mentioned in public all the time in the US. But there are places where it is not permitted - public schools for example.  Once again, it is doubtful that this causes loss of belief.