Just like what everyone basically said, it's because Toad kept annoying us by saying "The princess is taken to another castle" and that little make people say those two common words at Toad, but Toad isn't all bad because in Super Mario Bros 2 (US version), you at least control Toad and he is quite useful in some places, mostly if you need some strength, and some levels, you need some strength to get through the level.

And he also got his own game "Caption Toad" and that game is a hit. So, all and all, I don't think Toad is bad at all.

Toad isn't really much of a big issue to me. The only thing I hate about him like many others mentioned is the voice actress behind him that makes his voice sound worst the Homer Simpson's wife. Other than that, toad is just as respectable a character as any other Mario character to me. However, I'm pretty sure everyone has their reasons for why they don't like him. Not just for no reason now.

Its not hate so much as outright annoyance.  I don't mind Toad.  In the earlier games it was helpful at times and often would serve as filler.  But as the series progressed its voice grated on my ears more and more.  It was a perfect weight for me in racing but I select the Babies just to avoid hearing its raspy voice.

I enjoy puzzle games but I take long breaks between sessions of Captain Toad.  Its a shame...

I love Toad! The only Mario character I like more than Toad is Luigi. Toad has always been my favorite Mario Kart character as well, since the very first Mario Kart game. I've run my best races and had my best comebacks with Toad.

Also his voice is adorable! What are you guys talking about? Rock that awesome voice, Toad. Haters gonna hate. xD jk I do love his voice though, it's cute and happy which is what the Mario games are all about for me.

NO! NEVER! There are actually people that hate Toad??? NOOOOOOOOOOO!!!

This is the first of me ever hearing that people hate Toad. He was my favorite character in the Mario Kart series. Whenever I see him in any Mario game, he always puts a smile on my face. I have no clue what people are talking about otherwise XD

Personally, I do not hate Toad. I think that he is certainly an interesting character and fits the game well. I do not necessarily use him as my first choice when playing most Mario games but, is not that I do not like him I just don't think he jumps high enough. I am not sure if his big ole head has something to do with that. I do from time to time play him when playing Mario Kart as it really does not matter since most of the features for speed and so on depend mostly on the car and tires. I do like the little mini games in Super Mario 3D World where he has to collect starts and all you can do is move the camera all around to find your way- I am actually glad they made a separate game just for that and I would not mind playing it. I will agree that his voice is very very annoying lol. But, then again I think it fits his puny character. I like Toad and Nintendo is certainly exploring more of him.  I think he is a cute little thing just trying to help Mario and Luigi find the Princess.  <3 Toad

I hate Toad mainly for his voice. It's annoying, kind of like Daisy's voice, but much worse. That is the only reason I hate Toad. Other than that, he's fine. Oh, their worst is in Luigi's Mansion. They NEVER stop crying.

Hate? Why? Sure, he is mostly useless in the classical Mario games but I think he was mainly designed to be a supporting character. And he does his mission very well.

I think people hate him because he's a cute side character, just like the minions from despicable me, or the slugs from flushed away. Toad is a cute little side character that is quirky and funny and can easily be used for comic relief, as well as marketing. 
I personally don't have a problem with him, nor do I have a problem with minions or slugs. But people love to hate cute side characters, because people find them annoying, I guess. I think it's kind of an unjustified hatred.

Toads are a nuisance in Luigi's Mansion Dark Moon the levels where you have to rescue toads are my least favorite

The only thing i find annoying with toad is the voice as many mentioned before me. It just sounds like goblin troll mix noise that and for being bodyguard they sure do a bad job at protecting (even though it cant be a total thumbs down cause they do let Mario know)

The voice and the fact that they're all really poisonous

Answer: For the most part he was useless. The only time Toad was useful was if you needed strength and speed in SMB2. Like the desert worlds to dig through sand. He was bad at jumping and considering that the game is all about jumping that would lead to death after death. Toad was decent in Mario Kart,but he was a light kart and could be shoved aside easily. And his top speed was garbage.

I never knew people hated toad lol. My best friend always chooses toad for Mario Kart, and when we played Super Mario Bros for the Wii, we'd all kind of automatically go for Toad. 

I'm guessing it's maybe an ongoing joke?

I don't really hate Toad and I don't think most people do. What really bothered me was his voice in Mario Kart 64, that was the most annoying thing in my childhood. I haven't really played the new Mario Karts very much so I don't know if his voice sounds different but that was a big reason why I hated him when I was a kid.

I've always enjoyed playing as toad in any game that he's playable in.  Making fun of/hating on toad has become a meme in it's own right and I'm sure that's where most of the "hate" stems from.  As for hating his voice, I guess I can see that but it never really bothered me.

To be honest though, I don't find toad's voice being annoying or be angry because toad flips the finger on you. I mean, sure they changed toad's voice which is really irritating after Mario Kart 64, which is really more loud and a bit more high pitched than before, and sure he keeps on saying, "The princess is in another castle" and gives you the middle finger (which is actually a graphical error). However, he's at least supportive to Mario and his friends, and that's pretty nice, but also he has some few decent qualities to become a main character. Even making him one as the main protagonist, in Captain Toad. I actually find him pretty funny at times, and I like that about Toad as well.

To be honest, Toad is my favorite character to play as in Mario Kart. I love Toad, its so cute.

I don't see any reason why anyone would dislike Toad, his voice isn't annoying to me, and he's cute.

I guess I can see where they're coming from, but I just completely disagree with them on that. 

Toad is too ridiculous looking for his own good. I believe that the hatred for Toad started back in either Mario Party or Mario Kart either way Toad played a vital role in handing out stars to players if they had at least twenty coins in the first Mario Party game. They couldn't even get his voice right I always thought Toad was a girl because of his high pitched voice in Mario Party everytime a new star appears.