People have analysing books for their perceived messages and calling them dangerous for centuries. The reasons for the danger change, but it's pretty much always been there.
I think fiction can be a great way to explore and a focal point to discuss issues, but no, I don't think an awkward-unhealthy teen relationship in a children's book as 'irresponsible' on its own and it can be a great way to discuss things with children.
I think with Twilight there were some issues with adults praising the relationships as well as really misogynistic pushback that we see time and again with something that gets popular with teen girls. I think it can also be used to talk with teenagers, but it would need to be done with thought, not act like the literature by itself is damning people.
The harm in fiction comes when it's alongside wider social systems that give greater meaning. It can feel into wider problems in society, but on its own, it's no more dangerous than old fairy tales where parents murdered naughty children. Yes, that still happens, but the stories existing doesn't cause it, they reflect things that happen which can make it a lot easier to talk about.