Internet Hero,
I'm busy right now but I'll brief you on this. First, if you don't believe there was civil oppression in the US in the 50s and 60s, I'll offer Exhibit A.
Not exactly civil freedom. Not ironic either, when the corrupt state is the one outsourcing terror, which you'd be arguing if this was any other topic. Same thing with the 70s, as there was still a ton of civil unrest at the time. I'd include conscription in oppression of freedoms as well, so again we were not the beacon of light at that time.
On Colombia, they are a relatively free society, but they aren't very strong on property rights, a key freedom, or freedom from corruption. As I've previously stated, I'm for the decriminalization of drugs, so it's not a hard argument to make to show that those committing the terrorist acts feel that their livelihood is being oppressed (pick up the second to last Driveby Truckers CD for a poetic take on the black market and oppression). I don't agree with them, but I don't agree with terrorism, either.
In the 80s, you've discounted attacks on free societies by those from oppressive governments. At a glance, I'm betting you didn't include PanAm 830, which was an attack on the US by a Jordanian, or any attacks on free societies by folks like Carlos the Jackal.
My point is that terrorists are more likely to be from oppressive regimes. Not necessarily attacking them.
Here's a better source I found along the way as well. No little flags.
http://www.state.gov/r/pa/ho/pubs/fs/5902.htm
And another good article by Krueger.
http://chronicle.com/free/v49/i39/39b01001.htm