The arcades I went to in Akihabara was pretty family friendly, but I did go to a smaller one on the 3rd floor of an anonymous looking business building in a different neighborhood and it was a bit seedy, but it was just nerdy guys playing classic games and classic consoles and not dangerous seeming at all. I wonder if your gf's perceptions are colored by how conformist and competitive Japanese culture is. Of course those men are "losers," they are spending all their time playing children's games. My understanding is that men and women over 25 who aren't married there are seen as "losers" as well, and not being married and being video game obsessed must be a kiss of death in that culture.

As a child of the 80s I'm very familiar with the seedy arcade in the USA. I remember every machine having an ashtray wedged between controller and screen and that awful stink. I doubt the men there were regarded as anything but "losers" by the mainstream of the time as well. Being a capitalist culture, gamers weren't respectable until streaming and tournaments in which they could become wealthy. Money makes right in our culture. So our current perception of gamers is very far from what people thought back then who couldn't get rich playing games.