Dexter is very definitely not 'about' repressed violent urges. Its main character is a serial killer who feels a strong urge to commit violent acts, but those urges aren't meant to map onto (e.g.) suburban male angst or modern ennui or any of that Fight-Club-did-it-better stuff. The show presents Dexter's ritualized, even stagey killings as satisfying releases of psychic tension; if Dexter's 'dark passenger' were just a slick allegory for how Joe the Volvo Owner can't help wanting to hit his neighbour, then the moments of unexpected violence (that late-Season One confrontation with Doakes, the terrifying trip to the bar in Season Two, the initiating event of Season Three, etc.) wouldn't be as dangerous or meaningful. The times when Dexter gets pulled into unexpected violence are different in every way from his intimate nightly ritual...
...which is one of the least violent things on the show. In the world of the show, Dexter's murders aren't violent acts. In the killing room he looks as much like a man building a tiny ship in a bottle as a serial killer. When reviewers make claims like 'Dexter’s criminal “hobby” is a potent metaphor for those aspects of manhood suppressed by domestication,' I suspect they're grasping for an easy line rather than paying attention to the show itself. The arc of the show - a person with no access to 'normal' human feelings learns to be human despite himself, and joins the wide world - would still work if Dexter did something other than murder folks (it'd just be less spectacular TV).
Dexter isn't just 'repressed.' He's fully conscious of his cognitive shortcomings and miswirings and (during the run of the series) works to correct them, with mixed and intermittent success. In that regard he's more in touch with his feelings ('as a man' and otherwise) than pretty much anyone else on the show. It's a beautiful story, if you ask me, and not a bitter one.
[Hi Reddit types. Just so's we're clear: obviously Dexter is shown doing (what we know to be) violent things. But the meaning of those acts, in the show, in the story, isn't the knife-through-heart bit, it's the desire for ritual action - pure and simple - and how that desire gets complicated by Dexter's increasingly chaotic interactions with humans. He's learning to be a person rather than a machine for producing human-looking actions. The same show could be made with a rogue toaster over that goes around toasting household things, then finds out some foods would rather remain raw, and struggles to reconcile urge and event.]