If you are under 10, then you are already aware of what only a relative handful of your elders know: Robin can be really cool.
Where does the hate come from?
The problem is that for most people, my first experience of Robin is their only experience of Robin. As I grew and matured, I found other sources to feed my love of the characters, but most people have only ever seen the Adam West show and the (currently) 6 movies released since 1989 (of which Robin only featured in the worst two). Thus their view of Robin is somewhat skewed toward the camp and the buffoonish. The whole 'Robin is gay' joke that has been strung along in sitcoms like Friends, is one that has become cliche, but still damages public perception of the character. This of course stems from the 1954 book Seduction of the Innocent by American psychiatrist Fredric Wertham. Here he, essentially, suggests that all modern media is being created to warp children's mind and that violent and sexual themes have been hidden within the pages of comics and storybooks. He has created an idea that Batman & Robin are in a gay relationship and that Wonder Woman is a lesbian. His own pre-occupation with homosexuality in a time of repression aside, this is exactly the type of thinking that leads to claims of Marilyn Manson causing the Columbine shootings or Grand Theft Auto being responisble for car crime. Ill-informed, extremist scape-goating, yes, but damaging nonetheless.
More recently, I have been on message boards where people say that the love Batman, but hate Robin. How can you possibly hate a character that has been part of the mythos for nearly the entire publication history? Batman was first published in 1939. Robin was introduced in 1940. This is like saying you love Reggie Jeeves, but hate Bertie Wooster. You love Sherlock Holmes, but hate John Watson. To say that you find him uninteresting or irrating, fine, but hate? I think you might have only watched Burt Ward and Chris O'Donnell, little troll. Try reading some actual source material.
To use a very British comparison; to say that you hate Robin after only watching the '60s TV show or The Schumacher Batman movies is like saying you hate Miss Marple after only watching the new ITV series. You need to watch Joan Hickson or actually read some Christie to appreciate it.