The bad future shown to Ethan by Coach Ed in "Friday Night Frights" is already strange at first, but then Sarah comes in with Kurt. In that fake future, Sarah "marries" Kurt and they live together. Events further in the episode show that Coach Ed did not know that Sarah was only near Kurt to see if he had been bitten by Erica. However, it has never been mentioned whether or not Coach Ed actually knows that there are vampires in Whitechapel. Seems like he doesn't. As an example, if he knew Sarah was a vampire, he wouldn't have placed her in the role of a girl married to a "not-vampire". Really, this all boils down to whether or not Ed knows about vampires in Whitechapel.
From the Season 1 finale: why didnt Erica just remove the venom from Ethans arm? Story-wise, it makes sense to have Sarah do it. But the whole situation could have been avoided.
Several people die as a result of Benny and Rory's actions in "Flushed", some of them having disapeared without explanation. Yet neither demonstrate the slightest guilt or desire to inform the terrified parents that their children are dead. Are our protagonists all sociopaths?
Also, Rory is a vampire, therefore he would not feel guilt. (Listing two of the core five—and that doesn't even include everyone who was credited in the opening titles—so it's a little premature to say that the protagonists are all sociopaths.)
In the episode where Benny's evil twin is released, Evil!Benny goes to Ethan's house to warn him off. Were this not a Disney Channel show, it would have perhaps occurred to Evil!Benny that he would have had no difficulty luring Ethan to a secluded spot and killing him if he wanted him to 'stay out of the way'.