How do spells like Conjure Fey work? I mean, are we magically kidnapping unsuspecting pixies and forcing them to fight for us? Did a green hag mysteriously disappear from her coven and find herself the unwilling ally of an adventuring party? How does a mid-level spell have such a hold on every being in an entire dimension? Do the fey mind the fact that they could get pulled away at any moment? What if beings on another plane developed a Conjure Humanoid spell or something? Hm, actually, that sounds like a neat plot hook...
But seriously, this is kinda worrying. I'm sort of afraid to summon anything now. Maybe it's not as bad as it seems, and the summoned creatures are actually just mindless fey spirits taking the forms of regular fey when we call for them? But why do they get so angry when we lose control of the creature? They must not like what the spell does. Or maybe the shapeshifting fey spirits are just always like that, and will strike out at anything like a wild animal unless controlled by magic? This raises so many questions...