Why does Man-Thing seem to be so selective about who he kills? The comic keeps hammering home the point that Man-Thing is a mindless monstrosity, a beast of instinct that lashes out at anything that feels fear in range of his senses because fear is so discordant to his empathic senses. Well, given that A: he's a horrifying-looking muck monster, and B: he's a known killer that seems to strike out at random, who wouldn't be afraid of him when they first meet? You'd expect him to rack up a higher bodycount of innocents as a result of that.
When the comic says "fear", what it actually means is that Man-Thing targets people who CAUSE fear. It can tell the difference between someone who is afraid because a creepy swamp monster showed up, and someone who is already swamped with guilt and cruelty, and thinks the thing that just lumbered out of the swamp is holy judgement.
Depending on the Writer as well as Belsarios Maxim. In Deadpool Kills The Marvel Universe, he killed Taskmaster as soon as Taskmaster realized how horrible Deadpool's endgame was, so logically he should kill any hero he meets who's afraid of the villain they're fighting suceeding. Man-Thing himself is also in danger if he feels any kind of fear. Plus, heroes cause plenty of fear in criminals, and the average supervillian probably doesn't feel too guilty about what they do, and is more likely to assume Man-Thing is one of countless heroes or magical beasts in their universe than any kind of holy judgement.
It's usually established Man-Thing is The Empath. Burning fear is his main thing but he can discern other emotions a lot of the time to get a grip of who's a threat to him, who's not, the exact nature of the fear, e.t.c. The classic Man-Thing story "Kid's Night Out" kickstarts with Man-Thing's empathetic nature latches on to the kid's suffering and instills him with a sense of righteous vengeance.
The Film
Why everyone involved didn't do anything before Kyle arrived? To elaborate:
Pete Horn could have tried to stop the creature any time. He knew what it was, so what kept him?
Why didn't LaRoqe blow up the oil plant in the Darkwater that seemed to be the root (ha!) of all problems earlier?
Schists and brothers Thibadeux could have gone after LaRoque at any time, why did they wait so long?
I assume that Pete initially believed in what Man-Thing was doing, but by the events of the film came to realize that, yeah, this is going way too damn far, and I can't just sit back and expect things to work themselves out anymore (which was the attitude he displayed in the comic prequel).
In the comic prequel LaRoque was depicted as working for Schist right up until a little before the film begins. He presumably only started looking into Man-Thing and how to stop it just prior to and during the events of the film.
As mentioned above, LaRoque worked for Schist until right before the film begins, and so he only really became the prime suspect for what was going on after he took off. The brothers also had no reason to go after him until the Schists resorted to hiring them. They could have done it beforehand expecting a reward, but I think even they weren't dumb enough to think that Schist would give them anything without some kind of verbal or written agreement.
