So, NATO had a problematic operation, trying to establish (and coordinate the establishment of) guerilla stay-behind troops to use in the event of Soviet takeover - and the operation went especially problematic in Italy during the Years of Lead, where some of those guys associated with right-wing terrorists. The year was 1969 or so.

Basing on this, how do I conclude anything about the NATO of today?

Disclaimer: I was asked to hold an anti NATO speech during a protest event during a NATO summit. Being a moderately honest anarchist, I held a speech denouncing the practises seen in Afghanistan (the year was 2012), but emphasized that collective self defense is a valuable thing to have (a common attitude here in Eastern Europe), and added that if the alliance would bother doing what it says on the sticker, I would support it.

NATO is an alliance of various countries. Some of them aren't nice or democratic (classic example: Turkey). Mixed bag, and constantly changing. Membership in NATO is not a letter of indulgence for a member state to do anything - allies are obliged to help only if someone attacks a member state. If a NATO member attacks someone else, allies can ignore the affair or even oppose the member (example: Turkey recently bombed Kurdish troops in Syria so sloppily that threatened US troops shot down a Turkish drone).