Is trolling a sign of real-world cowardice?

Anyone who's been around the Internet for a while knows what I'm talking about. On almost every site, there's a handful of trolls that are there, not to offer anything constructive, not to prove their own expertise in any field, but simply to push your buttons, to say whatever it takes to irritate you and make you quit the site, to force the moderators off their duffs and into action. They'll say things they know would get them beat down in the real world, often derrogatory, racist, sexist, pushing and pushing constantly. Trolls are bottom-feeders. Since these nutjobs are using server space to spew the sort of inane and mean drivel they'd never have the nerve to say in real life, are they cowards?