Generally speaking, it's true that people over internet forums are generally more liberal in the US meaning of it (which I believe is the true meaning of it), and they are also more pro-european than in real life.
Of course, the fact is that on international forums you tend to go beyond the national way of thinking. What seems as an obvious truth in your own village suddenly becomes relative once in an international forum. As such, you tend to get more distance in front of the national "truth" on which many conservative values are lying.
However, the thing is that it works in both ways. Indeed, if you're a conservative from Nebraska, I guess you wouldn't be that much interested about what a French girl from Paris would think and there are strong chance you won't visit a forum where she can express herself. The same is true for a French guy working at the French rail and who's convinced capitalism is an evil invented by the Anglo-Saxons in order to destroy our specific French model. That guy wouldn't be interested in visiting an international forum.
As such, you see that there's some kind of natural selection that leads international forums to sound more attractive to liberal people, and as such, it can lead them to be more liberal afterwards.
