The Moment Dexter Went Off the Rails (And Never Recovered)
Well, at this point very many of the fans – and the former fans – agree that Dexter became a hopeless trainwreck at some point no later than Season 6. However, there is no agreement as to where exactly that happened.
Some say that Dexter spontaneously deciding to cut Hannah loose and have sex with her on the kill table was the point of no return.
Others believe that that Dexter running around college offices with an axe symbolized the end of smart Dexter written smartly and beginning of Dexter who gets away with all the murder and whatever because the plot says so.
And some think that the whole premise of Season 6's main antagonist was dumb and the "Debra in love with Dexter" angle was just embarrassing.
But perhaps the most popular opinion is that the show went off the rails completely and irrecoverably with Episode 12 of Season 6, This Is the Way the World Ends, in which Dexter finally confronts the Doomsday Killer, Travis Marshall.
That episode had multiple moments that stretch suspension of disbelief in quick succession, from Dexter escaping from shark-infested waters off Miami through sheer luck and Miami Metro correctly guessing where Travis was going to commit his last murder, despite being a few steps behind him up until that point, to a convoluted series of events which resulted in Dexter's son becoming Travis' chosen sacrifice.
But the moment which made especially many people raise their eyebrows came right after Dexter gets saved from the sea by a passing boat full of illegal Cuban migrants.
One of the men on the boat starts extorting others at a gunpoint. Dexter, somehow, concludes that the only way for him, personally, out of that situation is to kill that man. And then he easily does so, despite just spending most of the night in the water, holding onto a floating piece of a wrecked boat – a feat right out of an action movie, not a series which mostly pretended to be realistic.
And just as importantly, there we have Dexter, a man whose establishing character traits were meticulousness and caution, committing murder before a whole bunch of witnesses. Sure, the victim was probably not a man anybody would miss, and the witnesses were illegal immigrants, but he was still leaving a very obvious loose end. People who watched the series in hopes of, again, seeing smart Dexter written smartly were terminally disappointed.