
Some crazy fans considered it as "cheating" on them. But other fans, especially the older ones are more care about the idol's image, even as a fans they would be mindful of their own action (especially if they're fansite or fan manager) because it can damage their idol's reputation. Also, this is a public secret, older fans (noona/eonnie) like new rookie group more because they have this clumsy yet sincere charm, because the idol just debuted, they're still looking like they works really hard, so these fans like them even more (though they mostly leave the fandom after the rookie period ended).
In this case, dating scandal can be viewed as how they're insincere about their career. There are probably thousands group or soloist debuting each year, and only the top 10 can last for more than 5 years. Rookie is an unstable period where you need to constantly competeting with other groups that debuted alongside you. If they caught dating scandal, especially during rookie periods (and they're an idol group member), these fans would be thinking like "Are you serious? The other members are working hard to practice and get a job to promote the group and you have time to date?" or things like that. It really happens because I read the exact comments on Pann when a rookie idol have a dating scandal, though I forget which idol it is.
I don’t understand why dating is so taboo???