Is the Terrorist Glass Half-Full or Half-Empty?

The Tsarnaev brothers were clearly not criminal masterminds.... just criminals.  Mother Jones collected 11 Most Mystifying things the brothers did, ranging from what the younger brother wore to sticking around in Boston to running out of cash, and so on.  We will probably be able to add to the list as we learn more.  But for me, I don't know whether to feel more relief or more anxiety that these two guys were able to kill three people and injure more than a hundred people.  They were so, ahem, not bright, so does that tell us folks who do this kind of thing, self-radicalized terrorists can do some damage but not so comparable to an unregulated fertilizer distributor?  Or, if these anti-geniuses could do this much damage, what would happen if some sharp terrorists were atwork?

I can easily see either side of this.  The picture, I guess, is complicated enough that there are elements that should worry us and elements that should give us some solace.

In the worry category:

• that the younger brother was easily turned from a pretty decent life as a middling student with plenty of friends to an ally of his more messed up brother.
• that it only took two self-radicalized folks to disrupt the life of a city for nearly a week
• that despite their obvious cognitive limitations, they were able to build a bunch of bombs that mostly worked
• that they might not have been caught so soon if they were not such, well, idiots.

In the solace category:

• the Boston medical and first responder community was so competent that all of the patients that reached the hospitals alive survived
• that the terrorists would tracked down and contained within about 100 hours--the same amount of time it took the US to defeat Iraq in 1991.  We tend to be an impatient people, but that is some fast work. 
• that perhaps brighter folks are less likely to do this kind of thing because they are smart enough to sense that they would get caught, that maybe it ain't worth it, that maybe the US really is not at war with Islam even if it is in wars in Muslim countries (Bosnia, Libya are essentially pro-Muslim interventions, right?), and so on.  I guess there are plenty of smart folks who are radicalized, but they may still be deterred.
• perhaps more older brothers are not so messed up as to get their brothers involved in something so self-destructive.

Timothy McVeigh was much more destructive and not that much brighter.  So, is this progress?

I really have no clue how to think about this.  I am not an expert on terrorism or terrorists or radicalization or anything really related to this.  I am just a confused observer.  So, any clarity on this would be much appreciated, readers.