Plenty of displays have been legally challenged and removed.
Some have. But many continue without challenge. I guess it depends on whether they are seen as an establishment of religion.
Kids have been banned from singing carols at school or school-related events. My daughter was asked to pick her favorite holiday song to perform as a 3rd grader, and when she picked Silent Night, they told her she could not do that one.
As far as I know, this is mainly school decisions. Some schools have over-reacted to first amendment cases.
There has been a sustained, coordinated and uncalled for attack to create hostility towards religion in general and to seek to denigrate any religious-based values as improper.
That is the story that the religious right tells. But it is false.
The push for gay marriage, while possible having some impetus outside of that anti-religion campaign, is nonetheless a part of that.
It's my impression that the push for gay marriage is coming from the gay community, and is happening within the churches as much as elsewhere.
The religious right likes to paint a picture of religion under attack. Its a false picture.