I remember the centre of my local town being blown to shit when I was a teenager.
1996 is not that long ago. You really shouldn't discard it as 'the past'. What's funny is, large segments in the US actively supported these terrorists. All their rhetoric and they're just as guilty.
There's much less logistical support for various left-wing movements. After 2001, American authorities no longer approved of funding and supporting IRA operations in Britain so any hopes of "military" achievements by Irish nationalists dwindled. Also support for ETA and similar movements in Europe have declined.
RAF (Red Army Fraction) and various Arab groups used to work together; that seems nowadays negligible. But jihadist violence has increased its profile.
Yes, but I would say that the hope of any "military" achievements by IRA (in the sense of aggravating so much violence as to make UK give away North Ireland) was lost as funding and arms dealing was more difficult and surveillance more effective. So it was good sense to stick to the Good Friday agreement.
At which point does 9/11 not matter anymore?
I see this line of argumentation regularly, but since those movements were brought down with significant police and military operations, I don't see them as good examples for why Muslim extremism should not be brought down by police and military operations. There are other reasons, but this comparison doesn't qualify.