I suppose that just Otaku is a pretty general term so I should clarify the specific aspects I am talking about. I am referring to the people who are generally in love with anime to the point of obsession and people who have develop genuine romantic relations with dating sim games and 2D characters.
I can understand why people assume it is pathetic, you have a person who would rather collect items and form relationships with fictional characters compared to real people but at the same time I can't really blame them. I think everyone knows that humans can be cruel and some have faced cruelty more than others. I can see quite clearly why people who have faced cruelty, been worked to death, or worse would retreat into a fantasy world, I think everyone has retreated into some kind of fantasy at one point or another either through stress or just for fun. I can understand wanting the people who are damaging their health via this obsession, such as avoiding sleep and eating, but if a person is taking care of themselves, and they are happy retreating into an anime fantasy world at their home, what is the problem?
Japan's economic problems are likely not completely related to this phenomenon but it may also cause it itself because its making people overwork and thus not have time to form human relationships. I think America would run into a similar problem if people were required to work long periods of time. I remember hearing about a creator of one video game being so overworked and stressed out that he was actually given a limited period of time to live because of his health. I can't imagine being worked that hard and being able to handle anything, I mean even eating and sleeping might be pushed aside.
tl;dr. If a person is keeping themselves healthy, and are happy to retreat into a fantasy world and aren't harming anyone, why is that a problem?