User blog comment:B214/Volume 17 spoilers./@comment-67.176.158.104-20140320221310/@comment-4829046-20140321115452

To combat that downside is where you have harem management and family planning. Both of which are apparently being arranged(by Rias and her Mother), but won't be in effect for a long time. Well... in their defense, most of them are still in High School and due to their long lifespans, they don't really need to rush things. The only real reason to rush would be the ever impending destruction of worlds....