I'm split about this one. On the one hand, it's a little suggestive of some ego problem that you want your girl to be smaller just so YOU can look bigger.
On the other hand, as several have noted, there's a certain brand of hypocrisy in stating, "It's okay that I'm turned on by large cocks, because it's just the size of ONE body part, but if my appetite focuses on the size of the ENTIRE body, that's somehow condemnable." Put another way, I doubt very much that you'd be catching as much heat if you were a girl saying, "Sometimes, I wish my guy had a larger dick." Like many things, what's deemed acceptable is simply subjective.
Whatever your fancy, I think it's worthwhile to consider why you're with a person to begin with. We all have our preferences when it comes to physical attributes, but ultimately, we should hope that the foundation of a relationship is built on something a little more substantial. Still, purely as a hypothetical, if the OP could only get off mentally on really petite women, I think it would be a little two-faced of certain posters to hold that against him, when I've read them say things like, "Sorry, but I NEED a hung guy or I'm just not turned on," no?