Why would it be a bad thing? Isn't any women in a sexual fantasy a fictional character? And isn't an intentionally sexy/erotic cartoon character just a realization of that fantasy in real life?
Famous artists attempt to make photo realistic drawings of the female form all the time, with the hope that people can perceive it as arousing/attractive. Why is a cartoon any different? It may or may not be cruder than a photo realistic drawing, but if someone finds it personally attractive to them I don't see a problem with it.
Take Jessica Rabbit for example, she was designed to ooze sexuality and her face alone is coquettish and arousing to many. If it was wrong to be attracted to a cartoon character, why would Disney create her? Isn't Disney practically the public face of morality and personal values? Yes, I think so.
So no, of course it isn't wrong. It's human nature to recognize certain shapes and figures as sexual and attractive. There's no reason to be ashamed of it.