Yeah, why isnt there a thread?! It's almost as if the powers-that-be wont allow it!
BROTHERHOOD OF THE BELL (1970). The novel was adapted for a 1958 STUDIO ONE episode (which I've never seen), but the 1970 TVmovie is very 1970s. However, it is pre-Watergate, and I prefer it since government conspiracies are low-hanging fruit.
RACE WITH THE DEVIL 1975 INVASION OF BODY SNATCHERS 1978
The Groundstar Conspiracy (1972) Executive Action (1973) The Domino Principle (1977) Telefon (1977) Black Sunday (1977) Capricorn One (1978) Coma (1978) The China Syndrome (1979)
This is a master list of 1970s American movies which all carry the theme of "disillusion." Any urban paranoid political films ought to be somewhere here. (There's a lot to wade through though.)
Going outside of the U.S., many of the films of Costa-Gavras (Z, Special Section, etc.) immediately come to mind. France and Italy ought to have several under this topic too. I'll have to think about it.