I feel like you are getting overly offended by this situation. Here's some perspective. I hope.
Art has always been subjective. You think that you have a right to safely enjoy a work of fiction regardless of whether or not that fiction is in line with the moral values of a larger society. And y'know what, yeah, you're right. You are, presumably, a responsible adult and how you choose to spend your free time is your business. Conversely, the ratings board isn't really concerned with just you, the responsible adult. They are concerned with the moral values of the larger society. So, on occasion, they will attempt to prevent more fringe style art/entertainment from reaching a mainstream audience. This is not a bad thing if handled responsibly and only used in more extreme cases. And....
I would say that, yes, Gal Gun is kind of an extreme case. It is very much a piece of fringe art that, honestly, does not need to be available to a mass market. Luckily, for gamers like yourself, the title is still very much available via import sites like rice digital. It is easy to see why the publisher of the game is dissatisfied because this move will eat into their profits (and is bad press). You, however, should be fairly okay with it as it will not prevent you (or anyone else, really) from enjoying this work of fiction.
There will always be a place art that pushes societal boundaries. And there will always be a place to buy such art. It is folly to think that such art has a right or need to exist on a mass market store shelf. And really, the fact that it isn't readily available could even become part of the appeal of such works. One need to only look at the success of underground comics from R. Crumb to see that being denied approval from a ratings body is not the death sentence or slap in the face that you are seeing it as. It's simply the guardian of the larger society's moral framework saying, "yeah, this is a bit much for local (insert name of Germany's Wal-Mart equivalent)."
