As for Al Qaeda: I was at my school, New York Law School, when the two planes hit the World Trade Center about half a mile south on September 11, 2001. As I sat at my desk that morning I'd heard two thunks, which I thought at first were boxes being dropped on the floor somewhere upstairs -- but after I heard the news of the attacks I realized those were probably the two planes hitting the towers. As the morning went on, I stood outside on our corner and saw the towers burning, and then the cloud of dust from the collapse of one or both of them billowed up to about one small block short of where the law school sits.
And the IRA: I was sitting in my parents' flat in Knightsbridge in London when we felt or heard an explosion. That was the IRA's, or Provisional IRA's, bomb at Harrod's. I'd forgotten the date, but Wikipedia reports that it was December 17, 1983; I'd have been in England visiting my parents for Christmas vacation. Wikipedia also reports that 6 people were killed in that car bombing attack, including a U.S. citizen.
The IRA and Al Qaeda aren't morally equivalent. In a New York Times article reflecting on Representative Peter King, currently the scourge of supposed Muslim extremism in the US but formerly a strong supporter of the IRA, Scott Shane notes that the IRA's efforts mostly did not target civilians, whereas Al Qaeda obviously took aim directly at US civilians in the World Trade Center. I'd say the IRA's cause was more just than Al Qaeda's too, though it must be said that both groups had real oppression (Protestant rule in Northern Ireland, autocratic Arab governments supported by the US) to complain of, and in my opinion both were fanatical in their response.
A lot of very bad things have been done in wartime, and I think it's hard not to say that sometimes the end does justify the means. At the same time, a century's effort has built a body of international humanitarian law -- the more elegant and vague name now often given to the "law of war" -- that aims to minimize the means used, no matter what the ends, and that effort is profoundly important. By its terms, it is illegal for everyone to deliberately target civilians, and both the bombings that touched my life were exactly that. If Peter King doesn't see that these acts similarly deserved to be deplored, he's missing a crucial point.