From a personal standpoint, I am a big fan of Watarirouka Hashiritai and thus will really miss Natsumi. Not knowing as much about Rumi, her departure may not have the same impact to me, but everyone of the members has fans, and it is a sad occasion when the end to one of your favourite's career comes because of boyfriend scandals. But the agreement is that to be an idol in groups like AKB48 or Hello!Project, the girl must agree to have no boyfriends.
For girls who start at age 11 or 12, I think it is an easier agreement to make, as they probably don't have a huge interest in dating at that age anyway. But when idols get near adulthood, I would think some of them regret not experiencing dating during their high school years.
I just hate to see that the most memorable event in their career might be that they were forced out due to a scandal. Forgetting the years of rehearsal, grueling performance schedules, meeting fans at handshake events, smiling during performances even when they may feel ill or overworked, isn't fair, and their positive action and hard work is what they should be remembered and thanked for.