I think there's an Emporer's-New-Clothes / Common-Knowledge effect that differentiates the two. If a significant minority holds marginalized view X, but all such people think virtually no one else holds the view, then it's easier for a blogger to help the Xers identify each other and come out the woodwork (closet?) than for a lone pamphleteer.

Sure, but all they will achieve is to form an online echo chamber. To have real-world impact, they will have to establish themselves in the mainstream institutions of public opinion (principally media and academia). And nothing is a surer way to have the doors of these institutions closed to you than to be seen as belonging to some identifiable strongly contrarian cluster.

And if I may indulge in some mind-killing speculation, I think that's exactly what happened with libertarianism pre- and post-internet. Before, it was relegated to low-circulation newletters, with most adherents thinking themselves alone in the dark, and afterward it dominates internet discussion, a now mainstream medium.

Frankly, if you really believe that libertarianism dominates internet discussion, you have likely fallen for the echo chamber illusion.

Libertarian ideas have any impact only insofar as they have gained circulation in the mainstream media and elite academia, and I'm not noticing any increase in such circulation since the internet became widespread. (Notice that there is a vast chasm between these institutions and the internet libertarian circles, and people who manage to cross it almost inevitably do so only at the cost of becoming indistinguishable from the mainstream liberal or conservative positions.)