"Never fear. Him is here" - Captain Chaos (Dom DeLuise), Cannonball Run
Mace Windu: Then our worst fears have been realized. We must move quickly if the Jedi Order is to survive.
But for the OP in question. Since I aint Spanish but only live here, my perspective is a bit "from a far" so to say. I think personally there are many issues at hand. Yes there are some who want justice or/revenge for the atrocities of the civil war. Some want the Franco supporters to pay for their support. Others want to use the civil war to promote a new civil war (non violent) that will lead to the breaking up of Spain. While others want to remember but forgive for the good of the country so to say.
Pulling open old wounds like this is not uncommon to be honest. They still find mass graves and there are still pushes by local and national government organisations on top of the charities to exhume and identify as many as possible. There is also a push by some to remove Franco's tomb (which is frankly huge), and other symbols of Franco. About a year ago there was a computer game where it was possible to play either side in a strategic game to win the civil war.. that too gained a bit of controversy. Now we have this case. Many of the parents involved are in their 80s+ if alive at all.. what would you do to them? Throw them in jail?
As for the general amnesty. It is part of the process to heal the wounds of the civil war and the Franco dictatorship and move on. Most of the people involved in the setting up of the dictatorship and the civil war are in their 80s and above, and in poor health, that is those that are alive. They come from a generation where life expectancy is considerably lower than the average Spaniard today. Other than satisfy certain anti Franco elements that refuse to let the past stay in the past (mostly the left trying to taint the right wing parties with the Franco stain), what good is to throw an 80 year old woman or man in jail for being a supporter of Franco? As for those who participated in mass murder, well that is another story, but I understand that the law was put in place. After all, in a democracy like Spain with a very strong independent legal system, if you were to go after Franco's people for such crimes, then you also would have to go after the other side for the same crimes.
So sure talk about the horrors of the civil war and the life under Franco, but gunning for revenge ... bad idea especially 30 to 70 years after the fact.