The dangers of analogies
In your hypthetical grad class, Davin, it would be hard to ignore the interloper. On here, it's dead easy.
What do trolls troll for? Reactions, I would guess. If some individual is trolling and they don't get much in the way of a reaction, they will eventually go away. If, on the other hand, they manage to generate a lot of discussion (like this - damn!), they're happy.
A non-troll would be happy enough with a few links to good sources; if they don't learn from them, the links will no longer be forthcoming and they too will go away.
In other words - Don't worry (about Sam) - be happy!
My 2 bits.