To me, the whole ETA (País Vasco y Libertad) raison d'être became mute upon the death of Franco in 1975. From that point forward, their violence was just sadistic savagery aimed at women, children, and other innocents. Much like the Catalan separatists today, their arguments for independence are pretty weak as Spain is one of the most democratic countries in the world, not to mention a great place to live.
Overall, this series isn't very partial to the ETA cause and highlights their barbaric attacks over the years, focusing on the personal loss of the survivors. There is one incredibly painful and touching moment in E03 in which a man whose parents were murdered in the Hipercor supermarket bombing in 1987 is talking about how he took his newborn daughter to the cemetery and realized that she would never know her grandparents.
How could anyone justify these horrible acts against the Spanish people and government when the Basque people were free to map out a good part of their political destiny with the new constitution? That's what we call a rhetorical question. The ETA hierarchy should have looked around a little in Algeria during their stay there to compare it with the immense freedoms they already enjoyed in Spain. For them to use terror and violence to achieve their political goals was inexcusable.
It's impossible for me to see the ETA leadership as anything other than bloodthirsty filth and bullies who hide in the shadows. History will judge them as cowards and murderers.
For me, this series was a great education and opened up an entire can of worms of new avenues of study, books to read, movies to watch.