Mineta is hated because he's a pervert but not for the reason you think. Being a whiner and pervert is his entire personality if not his entire character; other anime perverts like Sanji, Jiraiya, and Meliodas have other traits to them, All three are great fighters and they have backstories, Jiraiya is a wise mentor and father figure for Naruto, Sanji is a man wanting to achieve the dream of his surrogate father and wanting to separate from his family's evil name, and Meliodas is man who betrayed his family for his lover and who is now forced to watch the woman he loves die, be reincarnated, then watch her died again while seeks a way to free him and his lover from the curses put on them. Also Meliodas only does perverted things to Elizabeth aka the love of his life. Mineta's lack of a backstory makes him unappealing to the audience because it means all the Reader/Viewer knows about him is that he's a pervert. The three I mentioned also can show restraint; when it's time to fight or be serious the three can hold back their perverted thoughts and actions Mineta however never does that. During the USJ attack he acted perverted towards Tsu.