Citation: http://www.straitstimes.com/breaking-news/asia/story/osaka-mayor-wartime-sex-slaves-were-necessary-20130514
His statement is on the assumption that Japanese solders were required to stay at battlefields for a long time.
It is clear that one of the faults Japanese military caused is that the authority deployed solders at battlefields longer than other countries' authorities did.
What we should discuss is not whether prostitutes were needed or not, but how to create environment of battlefields where prostitutes are no longer needed.