I can imagine people saying stuff deliberately to stir shit up. There are assholes everywhere, and being on the internet just makes them feel more powerful for some reason. But that's not everyone. I know plenty of fans who badmouth ships they don't get. On every side of the fence, mind you. I'm not singling any one group out. I know Arthur/Gwen shippers who do it to Merlin/Arthur shippers, as well as vice versa. Bangel vs Spuffy. There is no group exempt from this kind of behavior.
But why? Why waste the energy? Why pour that much vitriol into something that ultimately has little to no effect on you and your daily life? I just don't get it.