Are terrorists really cowards?

With the Boston Marathon bombing, as in the case of virtually every other terrorist attack against US interests, the politicians and talking heads refer to the acts as "cowardly".

But is that really an accurate assessment?

I think launching a terrorist attack takes some major cojones, and a very strong commitment to one's own values, for better or worse. Isn't that the opposite of cowardice?

Accordingly, I wonder if perhaps the "coward" label is maybe thrown out there loosely in an attempt to make the perpetrator feel small, which might lead some of the more mentally/emotionally unstable of them to make a mistake that might result in their detection and prosecution. (This doesn't make it wrong.)

What do you think?