I have been talking with an expert on Basque nationalism and terrorism who teaches at my former university.
He told me about the very different profiles from ETA members in the beginning of democracy (when it killed someone aproximately every two or three days) and nowadays.
- The first generations were highly specialized workers with a medium-high life standard.
- The present generation comes from teenagers from problematic neighbourhoods, with almost no culture/preparation and very well known to the Police, since they started as teens to take part in "kale borroka", what they call street fight and is nothing more than pure vandalism. They have no real interest whatsoever in politics, their only ideology consists in a few ideas tattooed in their brains.
The man who told that to me, also explained that old ETA members had trouble if they tried to talk some sense into them. They were accused of being fascists!!
How is that important?
The older generations, if/when they wanted to leave terrorism, they could find a nice job and their place into society.
What would the newer generations do, even if they were looking forward to really leave that life behind? Underground activities, hatred and violence (at least in a social level) is all they know, they donīt know how to do anything else. They also have been getting quite a good salary from ETA and are used to it and all it gets them.
Can they give up all that? Will they be able to quit for good, accept a job with a much lower wage than the one they have now, and donīt miss what they lost?
How can we be sure they wonīt turn to other crime branches? There are plenty blossoming in Spain in recent years.
What is going to be done with all that people?
Maybe we should think about that before we stop arresting them and/or start freeing them.
I'd like to draw two parellels:

1. The first members of the Ku Klux Klan in the US were middle-class men just getting together for some wierd fraternity-type stuff, whilst taking out their greviences about blacks. The second and third gneration of members were the ones we tend to remember. They were the militant kind - younger, poorer, with a problem against the world in general and no real way to constructuvely channel this built-up anger. But this generation weren't nearly as violent as people believe even today. Murders of blacks fell consistently through every decade the KKK was around. In economic language, they had "credibly established a reputation as killers" and therefore noone tried to find out if this stayed credible because they were simply too scared. Maybe politicians now in Spain that give in too easily to ETA are doing the same?
2. The black ghetto population in the US in the 1980s: Being black was a disadvantage until the 80s - you were poorer than whites, less educated, more likely to have social problems like drug addiction/ teenage pregnancies etc.
However two things stopped them freeing themselves from this trough. First the "dont try and be white" syndrome. If a black person went to a white-dominated school (white=better generally) or tried to speak more enunciated, "proper" english without typically black slang or just tried to be less "black", he was a social outcaste. All his black peers would pick on him, bully him etc. Even though everybody complained of the terrible conditions they as blacks had to endure, dragging themselves out of this was the equivalent of social suicide: youre too white for the blacks, too black for teh whites.
secondly (and this is far more controvresial...for those who dont believe me read economist stephen levitts brilliant book freakonomics), the emergence of crack cocaine as a cheaper, more accessible form of cocaince that made you high very quickly in the 80s destroyed any blacks had of, en masse, freeing themselves from the poverty. there was big money to be made here (more than in any job they could feasibly otherwise get). it money more than outweighed the risks. hordes of innercity black teenagers turned to dealing and using. of course, this didnt make them all into millionares like they thought it would.
similarly with ETA. the newer generations wouldnt be able to integrate well into the non-ETA part of society, or at least woudlnt be able to break the links well. therefore they stick with their terrorist group. however, just as it was easier for the LAST generation to leave ETA than it is for the current, itll be harder for the next gneration compared to the one now.
unless someone takes th emoral high ground and lifts them (whether they want to or not) out of their vicious circle. and by this i mean the government. of course i also mean making significnat concessions
oh...one last thing: there still wouldnt be any guarantee of peace.