Not a lousy behavior necessarily, liking a two-dimensional girl is not a big bad thing, as long as it does not affect their normal life and other people's career, and not affect their own progress, such behavior should be lenient by the public. But some people especially the older don't know how to comprehend feelings of otakus. In a word, they think that there are too many otaku men who are not accord with their aesthetic.
In fact, even the group of otaku men also have outstanding figures in all aspects. In Baidu Post Bar, I also saw a super student who won the first of college entrance exams wearing a T-shirt printed with cartoon characters. Most of the otaku men who were thought be lousy just because they failed in their career. If a successful person likes 2-dimensions world, others will think that hobby is icing on the cake. We don't have to use colored glasses to look at others, which will lead to our view of a group deviate from their actual situation.