“Did you notice the fountain of blood on Hollywood Boulevard?” asked my wife, when she returned home from a shopping trip the other day.

I told her that no, I had not noticed the fountain of blood on Hollywood Boulevard. “It’s cordoned off with police tape,” she said, “and some detectives are giving away sets of kitchen knives.”

She wasn’t kidding. It was, of course, a marketing stunt – played out across 14 cities in the US – to promote the new season of the TV show Dexter. Or “the return of America's favourite serial killer”, as the red-white-and-blue billboards cheerfully put it.

For those not familiar with the most critically applauded TV show since The Sopranos, Dexter is a comedy-thriller about a police blood-spatter expert who just so happens to stalk and kill people on his nights off. The phrase “loveable rogue” comes to mind, although I’m aware that this phrase was once associated with Ian McShane as Lovejoy, not a man who wraps people in clingfilm and dismembers them.

All of which makes me wonder: in a country where the authorities are still enraged by a fleeting glimpse of Janet Jackson’s bejewelled nipple, how can a serial killer become a primetime TV hero?

The answer, I think, can be found in the way pop culture has celebrated the serial killer since the phrase first emerged in the 1970s. Indeed, we’ve become so overfamiliarised with the horror of extreme antisocial personality disorder that serial killing is now regarded as an almost comic affliction, like Tourette syndrome. Just the other day, I was watching a rerun of a weepy father-and-son TV interview with Lionel and Jeffrey Dahmer, which I thought must have been a skit from Saturday Night Live. “We never really had a real deep heart-to-heart talk about what was going on inside our own minds,” Dahmer said to his father, who sat next to him, nodding stoically. Dahmer, I should point out, murdered 17 men, had sex with their corpses, then dismembered them. Oh, and he ate them, too. “I just sort of lived in my own little fantasy world,” he told the TV camera from inside prison, with a shrug.

Are we in danger of becoming too comfortable with the Dahmers of this world? After Dexter, what’s next - a sitcom about paedophiles?

I’m glad to report that such worries disappeared when I sat down to watch the new Dexter on Sunday night. It was then I realised that Dexter isn’t really a serial killer at all. After all, he only kills people who “deserve” to die. And that, in my book, makes him an altogether more traditional and reassuring figure. It makes him a cowboy: the masked vigilante, dispensing justice his own way. Which comes as a relief, because I was started to feel a bit queasy about rooting for the bad guy. Now I just think of Dexter as another modern day version of Jack Schaefer’s Shane – if Shane had clingfilm, an empty warehouse and a collection of power tools.

Times Recommends

• Police beg us for food. What hope is there?
• Moral darkness that engulfed Baby P
• More to Advent than cheap chocolate