As a resident of South Louisiana who a long time ago went fishing with my father, I can define the ORIGINAL meaning of "trolling."
You take a really low-powered outboard motor that is enough to overcome a light current that might make you drift, but it isn't big enough to start a big ruckus in the water. Don't want to disturb the fish, you know!
Then you drop a line in the water and see what nibbles. You hope that the bait is good enough to attract your favorite fish. The fact that it is moving slowly against the current gives the illusion that it is moving under its own power.
Of course, from the fish viewpoint (Internet OR aquatic), nothing bad happens to you until you open your big mouth and nibble on the bait.
Combine THIS meaning with the mythological reference to "troll" - a creature who lurks under dark spots under bridges and waylays unwary travelers - and you have the perfect definition of a troll in the Internet sense.