There's nothing wrong with Young Adult romances. After all, first loves and hormones are all part of the teenage experience. However, looking at the last couple of years of YA novels, it seems that romance has shifted from being a genre trend to a genre requirement -- and the genre has suffered for it.
I've since come to treat the YA romantic subplot as the pit in the center of the narrative peach -- an awkwardly placed and inevitable annoyance to be endured and avoided while enjoying the otherwise interesting plot.
For every one YA novel with a well-integrated and beautiful romantic element, there seem to be three where a romance or, worse, a love triangle is gracelessly shoehorned into a story that neither requires nor develops it. As a result, you get novels with underdeveloped characters, abbreviated plots, romantic progression that relies on irrational and often abusive behavior, and the dreadful phenomenon described by reviewers as "instalove." The shy, outcast girl looks across a room and catches the eye of a mysterious, moody loner boy and bam! Instant romance! Just in time to fight the Evil Cow Zombie Overlords of your Dystopian Future Setting.
These tropes are particularly noticeable in the subgenres of science fiction, fantasy, and dystopian YA novels, where there's already a "serious plot" that requires the lion's share of the narrative -- leaving little enough room for a romance. Using "instalove" seems like an easy way to market your novel as "The Next Twilight" and land a girl in a flowing prom dress on your cover without having to waste words actually developing a relationship.
Here's the thing, though -- you shouldn't write a multi-genre novel if you only respect one of those genres. I cut my book reviewer teeth on romance novels before venturing into Young Adult territory and I can tell you that your futuristic revolutionaries, genetically modified cheerleaders and half-angel Mathletes could learn a thing or two from those raven-haired hoydens and scandalous Dukes.
Romantic stories are ultimately character-driven rather than plot-driven -- they depend on character progression and escalating interaction. A lazy romantic plotline can still have a negative impact on the "serious plot" if it compromises the realism and development of the characters.
Take Gennifer Albin's Crewel, for example: an ostensibly "feminist" futuristic YA about a heroine who can alter the fabric of reality. But what does it say about her when she spends the majority of the book whining and mewling between two equally bland and shallowly drawn love interests instead of actually, you know, changing the world or fighting The Evil Establishment?
That's not to say that YA plots can't accommodate and benefit from a well-written romantic plotline. Look at Rachel Hartman's award-winning Seraphina. The novel has a "serious plot" (investigating the suspicious death of a prince) that brings our two protagonists together in a situation that allows them to discover the other's skills, fears, and motivations. Seraphina's and Prince Lucian's feelings develop organically as a result of their participation in the "serious plot." As a result, the romance is realistic, charming, and directly supports the central narrative.
Then there's Code Name Verity by Elizabeth Wein. This brilliant historical YA is one of the rare titles to come out recently with no romantic aspect or love interest at all. Would a romance have fit into this story about World War II spies, torture, and female friendship? Would it have been worth it to sacrifice scenes of the protagonists' platonic bond in order to tack on an affair with a mysterious, moody Resistance fighter? Not really.
What I'm ultimately saying is that romance is not intrinsic to the Young Adult genre, nor can you blindly play Pin the Love Triangle on the YA Plot Line without affecting the entire narrative. A romantic subplot requires just as much narrative investment as any other aspect of a novel. If a romance doesn't directly contribute to your central narrative, don't add one. In literature, as in life, you shouldn't embark on a romance unless you mean it.