So MB, you were ok with the Leviathans but it was the threat of Phillip Todd being hung that made the storyline ridiculous... LOL.
This always bothered me as well. It's lazy writing when proper research is not done. Maybe my experiences are skewed because I was around a lot of talk about capital punishment and I was aware that my home state, Rhode Island had pretty much abolished capital punishment since the early to mid 1800s. There was one provision. IF a person was serving life without parole and IF that person killed again, that person might be executed. No one had been in all that time. I was also well aware that Maine had no death penalty either since long before 1897, so Minerva Trask's threat to Rachel was also sloppy writing.
What always bugged me was how, in TV and movies, people were much more likely to get the ultimate penalty than they were in real life. Even on Star Trek, Spock is facing DEATH for going to Talos IV. This made no sense. Let's have a death penalty for going there. We won't tell anyone why, just don't go there. Let's make it forbidden fruit. Wouldn't it make more sense to just keep quiet about it, and label it hazardous?
The real reason of course is the mistaken idea that this kind of lazy writing leads to more SUSPENSE. I can tell you, I found the episode Court Martial just as "suspenseful." Kirk was not facing the death penalty. He was facing the loss of his career and disgrace.
This is a round about way of getting to your point, it doesn't matter if a plot is totally impossible and absurd in the light of day. The more realism you inject into the story, the easier it is for the viewer or reader to immerse him or herself into the situation. Stephen King knows this, as did Bram Stoker. Works like Dracula and Salem's Lot seem more realistic and vivid because they exist in a world that's just like ours except for the vampires.
That's my take on it anyway.