One thing needs to be clarified: "troll" does not mean someone that criticizes harshly, or someone who misses you off. A troll is someone who posts things for the soul purpose of angering people.
If someone is criticizing something that you love, but they're doing it because it's how they really feel about it, and they're just venting that feeling; then regardless of how much it bothers you, or how harsh their wording, that is not trolling.
The word gets used incorrectly a lot in this time of hyper-sensitivity, and I think this comics is included in that. The first person pictured seems like he's probably trolling, but the guy saying he hated the casting choices in the movie he saw? That's not trolling. That's just sharing a negative opinion. Not the same thing.