This is my opinion. Feel free to disagree with me, but please do so respectfully. Thanks.
I think fairy types are OP (overpowered). I know that some people may love fairy types and some people may hate fairy types. I don't love nor hate fairy types, I simply think that they're OP. I don't use fairy types on my team, but I have used a fairy type move for a while when my Ralts was young and it was a good move. But when it comes to battling fairy types, that's when things start to go downhill.
I understand that dragon types were OP in the first five generations. I love dragon type Pokemon, and would always use one in my team. They are kind of OP. I went against the dragon type Elite Four member in Pokemon Alpha Sapphire (forgot what the guy's name was) and I literally one shot his entire team with a mega evolved Latias' Dragon Pulse. Plus, dragon types have high defense against the elemental types (fire, water, grass) and only have two weaknesses (ice and dragon). So I can see why fairy types were needed. FAIRy enough (haha... ha... ok sorry)
My reason why fairy types are OP is most likely biased, so it's not the best reason. But honestly, fairy types ruined my Pokemon experience. First of all, it was a new type, and I didn't play Pokemon X or Y, so when I got Pokemon Alpha Sapphire I was inexperienced with all these pretty pink Pokemon. It also threw me off that some older Pokemon had fairy type as a primary or secondary type. My personal reason why fairy types are OP is mainly because they make dragon types useless and they only have two weaknesses: poison and steel. There aren't that many powerful poison or steel type moves. I don't use poison type Pokemon at all, and I only use steel Pokemon for the defense, not for the offense.
But like all things, there are cons for fairy types. Bulbapedia says in its article about Fairy types:
So I'm not angry that fairy types were created because at least they're still a somewhat balanced type."Despite having numerous advantages, the Fairy type is a balanced one due to the lack of particularly powerful Fairy-type moves, being somewhat weak statistically and having a disadvantageous match-up against the Poison and Steel-type, two of the best defensive types in the series. Also, since Fairy types typically have high Special Attack and Special Defense, but relatively low Defense and Speed stats, they have advantageous match-ups against most special attackers, but poor ones against physical attackers, overall."
Overall, though, I'm not very happy with fairy types. Every time my Gallade gets Dazzling Gleamed I scream.
On the bright side, they're pretty.
Sorry if this entire post made no sense at all. I'm usually not very good with words. Both in real life and on the Internet.