What is happening hete is that the protection of fans' fragile fantasies automatically trumps the basic human right to a life outside that fantasy framework. Though as lawyer Hifumi Okunuki pointed out in a Japan Times article on Jan. 22, such an arrangement is probably illegal under Japanese labor laws.
The central prpblem of groups such as AKB48 is the defence that by dating, idols are ruining fans' fantasies. This is key to understanding not just AKB48 and their sister groups, but pretty much all idol culture. The groups are not just selling music, they are selling a fantasy narrative. It's one that everyone knows is fake, which is why it is imperative that fans' suspension of disbelief be maintained at all costs – with severe punishments for those who step out of line.
The deeper truth is that idol fan culture, as well as the closely related anime and manga fan culture, is institutionally incapable of dealing with independence in young women. It seeks out and fetishizes weaknesses and vulnerabilities and calls it moe*3, it demands submissiveness, endless tearful displays of gratitude, a lack of confidence, and complete control over their sexual independence. AKB48 takes this a step further by allowing its (largely male) fans to sit in annual judgement, voting members up or down in the group's hierarchy*4. The danger is of this fantasy creeping out more widely into society: Japan currently ranks at 101 in the world gender-equality rankings (79 places below the United States, 32 below China, and two below Azerbaijan). What will a 13-year-old girl think when she sees a humiliated member apologizing for natural human behavior?