Why do so many people hate the Detective Boys?

[Dwalin]

That question has been bothering me for a very long time. What’s so hateful about them? They are not as clever as Conan, they disturb him during the investigations, but he often provokes them himself by not being sincere with them: instead of frankly telling them he doesn’t want them around he pretends to be their friend but then, when they stumble over something important, he always leaves them behind without even bothering to make up a convincing reason to keep them calm. It’s a natural consequence that they get envious of him.
They also may be considered useless by somebody, but that still seems too weak a reason for really HATING someone.
To be honest, I cannot think of other reasons for hating them.
So why do so many people hate them? I just don’t get it.

[Vylash]

In my opinion, they're nothing more than an annoyance

[TypeSera]

Personally... most of the time, I just couldn't really connect with them anymore - I'm already 25 and feeling a little tired of seeing so much kids.

[Stopwatch]

I think it's more that people aren't used to kids that much and think that the characterisation isn't that good. For example, Genta is obsessed with food, it may be more toned down than in earlier volumes but it still makes up pretty much most of his character. Plus there's much more interesting characters and, like TypeSera said, most people find it hard to relate to them. I think they're okay, I'm sorta neutral to them...

[KaitoGirl]

They're just filler cases -w- but hate them as characters... I really don't think I hate them, they're kids after all though I don't play with kids like them I like kids  they're innocents creatures.

[Wakarimashita]

It's true that I don't like Genta, but I'm not really bothered by Ayumi or Mitsuhiko and I think Haibara's a pretty good character.

[Dus]

The Detective Boys were introduced to appeal more to younger audiences. So, they simply do not appeal to older audiences as well.

[Commi-Ninja]

I don't like children in general and Ayumi and Genta especially get on my nerves.

[Arisana]

I feel that the anime has a hand in making the Detective Boys (Haibara exclusive) seem worse. Instead of animating the case that led them to develop a partly forced friendship with Conan, introducing them too early on in the anime makes them appear to be a more forceful group than they actually are. (How they followed Conan to the Okino Yoko case and tried to force friendship onto him made me cringe.) The children have their own qualities that some may deem annoying, but strictly canon to the manga, they aren't quite as bad.

Their worse quality seems to be their inability to realize that they are children. But then again, it is likely typical of kids to think that 'if this person can do this, why can't I?" Particularly so when Conan's apparent age is the same as theirs. This seems to hold true more so in the manga, once again. I remember that while those three kids were particularly ruthless, they weren't quite so much prior to meeting Conan. (At least, they didn't aspire to become detectives before then.)

It's possible that people dislike children too. But whether Gosho added the Detective Boys to give Conan camoflage or to appeal to younger audiences is debatable. Likely both.

[Xytan]

People hate the Detective Boys because NOTHING INTERESTING EVER HAPPENS WITH THEM.

We don't have this captivating suspenseful chase with the Black Organization, or a triple homicide with Kaitou KID.

We just have a bunch of kids searching for a Cat.

I do not read DC for that.

[Wakarimashita]

That's a matter of opinion, I prefer DB material to most Kid cases (especially the recent ones) and the "Blue Castle Case" is better than a lot of BO cases.

[Abs.]

"Hate" is too strong of a word here. Perhaps many people would prefer the Detective Boys to not appear as often in DC, but to hate a fictional character is a bit much. To hate a real child even more so.

Also, I edited the bad grammar in your subject title.

[Commi-Ninja]

I dislike children as a whole, and only a few specific ones do I actually despise enough that it could be considered hate.

[Abs.]

I dislike children as a whole, and only a few specific ones do I actually despise enough that it could be considered hate.

Hate the parents, if you have to hate someone.

[Shuusgirl]

I feel that the anime has a hand in making the Detective Boys (Haibara exclusive) seem worse. Instead of animating the case that led them to develop a partly forced friendship with Conan, introducing them too early on in the anime makes them appear to be a more forceful group than they actually are. (How they followed Conan to the Okino Yoko case and tried to force friendship onto him made me cringe.) The children have their own qualities that some may deem annoying, but strictly canon to the manga, they aren't quite as bad.

Their worse quality seems to be their inability to realize that they are children. But then again, it is likely typical of kids to think that 'if this person can do this, why can't I?" Particularly so when Conan's apparent age is the same as theirs. This seems to hold true more so in the manga, once again. I remember that while those three kids were particularly ruthless, they weren't quite so much prior to meeting Conan. (At least, they didn't aspire to become detectives before then.)

It's possible that people dislike children too. But whether Gosho added the Detective Boys to give Conan camoflage or to appeal to younger audiences is debatable. Likely both.

Exactly what I was going to say, but you said it better. 
Most people say that nothing happens when the DB are around, which isn't always true, but for sure is in the anime.  After all, when it goes, 'bunch of canon DB cases, AO DB cases, AO Mouri case," before hitting anything important then I think it's boring too.  But they're really not that bad, and some of the DB cases are important.  I used to read DC every night before bed until I caught up, and my sister had already caught up and tried to get me to skip the DB ones.  Turns out, one of the ones she tried so hard to get me to skip was really important.