I think it just depends on how they see a certain character, be it be a physical attractive or something of their personality they like. Perhaps these cartoon characters fit the quality that people like to be attracted at. I have no problems with people having affection for cartoon characters. Heck, I have a few myself: for example, at the current moment, I find the character Vlad Masters/Plasimus of Danny Phantom to be quite the attractive fellow (older man, nice hair and suit, eyeliner eyes, soul patch) with an engaging personality (suave, clever, complicated enigma).
That said, I DO get worried if people start to treat them as real-life people or any of that form of obsession. I think there's a certain line you should cross when admiring a cartoon character because in the end, they ain't real.