A nostalgia is harmful if it prevents action if it leads to condemning the present in a distorted way if it distorts and beautifies the past without understanding it correctly. 

In Contrast, nostalgia is beneficial when it collects from the past the good when it denounces the loss of valid principles when it points out the mistakes that have harmed the people and the peoples.

There are, then, bad Nostalgias and good nostalgias. The first Ones generate sickly mistrust. The second one allows a healthy critical spirit to wrong choices that generate malignant processes. 

The above applies to people and human groups. A person can look at his past and idealize it without respect for the truth while lamenting his present situation to the point of not recognizing the opportunities that she offers.

Or that person can also analyze the past and see that there have been good things that deserve to be empowered, and mistakes that need to be corrected. It will Even come to that healthy nostalgia that serves to recover ancient treasures that are always worth.

In groups there is a risk of disfiguring history, to exalt leaders who were nothing exemplary, to imagine that before things went well when a little objectivity denies distortions that distort and allows to see that in that past there were evils In need of healing.

It is not easy to correctly compare the past with the present, nor avoid erroneous nostalgia. But when an analysis carried seriously recognizes in the past treasures such as respect for life, the defense of marriage, the affection for grandparents and parents, the authentic desire to love God and others, we can come to a healthy nostalgia, that will drive us to promote those treasures in a present that needs them peremptorily.