Agreed. However, we do not presently face anything remotely similar to the United States being "destroyed." Those who say we do are using hyperbole. Even if the terrorists get hold of a few (or a few dozen) nukes and actually use them (not a particularly likely scenario) it would not mean the destruction of America. 10,000 nukes launched by the old USSR, that would have been the destruction of America. The threat we face today, in comparison, is merely annoying.
So we return to the ancient argument about whether the end justifies the means.
If you say that a "good end" justifies any means, you essentially join the Commies, who believe that any crime, no matter how enormous, is justified if it advances the goal of Communism by the tiniest amount. In practice, of course, this means that any action whatsoever is justified.
Those who refuse to allow that certain unpleasant means are justified by certain noble ends fall into the pacifists trap, in which maintaining my own moral superiority far outweight all possible conseqnences, no matter how great.
I think most thinking people are left with the uncomfortable realization that certain greatly important ends justify almost any means, but also that the slippery slope inevitable in war tends to a constant reduction in exactly how important the end that justifies horrific means is.
I believe our attackers are restrained from the physical destruction of our population at large only by their present capabilities, which will only grow unless we drastically change our course of action.
We recently saw our enemies' capabilities leap by several orders of magnitude, and it should be obvious that indiscriminate mass murder is their modus operandi. Another leap in capability will reasonably result in the death of millions and millions if you consider the biological technology sought, if not owned by our enemies, and the nuclear technology which is proliferating rapidly not just to terrorists but a number of states, including China who see the existence of America, as an ideology, anathema to their success.
The unfree world is dominated by tyrants who are unrestrained by moral ambivalence about mass murder. We stand as a beacon for democracy and as such are a threat to tyrants everywhere.
Believe me, if we only respond to this as a bombing, without looking at the long-term trends and implciations, we will see our destruction. If not by the physical death of millions of Americans, then by focring us to install tyranny here in order to save our own lives.