The amount of propaganda that inundated wartime Japan was rather astounding. Even senior civilian officials lacked an accurate picture of the front lines. This isn't to say that they were unaware of the brutality of the Japanese advance-for instance, here are several contemporary newspaper articles referring to a contest where two Japanese NCOs had a contest on who could kill 100 people with a sword first-but it was sanitized substantially. For instance, it is implied that the above contest was of two soldiers seeking to emulate their ancestors and reject modern warfare in favor of hand-to-hand combat, rather than an outright slaughter of random people.

In that line of thinking, your typical civilian, if they were aware of the presence of Japanese, Korean, or Chinese women serving as comfort women in the front lines, they likely would have assumed that they were merely prostitutes that have been organized by the military to help care for the soldiers at the front. Some civilians may have even stated that it was necessary to reduce the amount of rape (which one only needs to look at what happened to Nanjing to see how ridiculous this is) by providing a legal alternative-one need look at the post-war Japanese government's establishment of the Recreation and Amusement Association during the Allied occupation. This organization was established primarily to reduce the incidence of rape by instead essentially coercing some Japanese women to serve as prostitutes for the occupying troops. Sadly, it may have even been somewhat effective-the amount of reported rape rapidly increased after the system was basically shut down a few months after its inception. It is also important to note that the typical Japanese person viewed the entire China campaign as not a campaign of conquest, but a campaign to restore peace in China and to overthrow the corrupt and fragmented Chiang Kai-Shek regime.

Source:

Dower, Embracing Defeat, Japan in the Wake of World War II

They would say yes, it was a good idea, because it would cause the troops to behave in a better manner. You have to understand that at the time, women had no right to their own bodies. It was legal and quite common in Japan for a parent or guardian to sell their daughter into sexual slavery. That's how most prostitutes became prostitutes. The practice was only made illegal after the war by the U.S. when an American woman, who happened to be a feminist, Beate Sirota Gordon, was put on the committee to draft the new constitution, and insisted upon including women's rights in there. You have to also understand that in Japan, as in the West, if a woman was a prostitute, regardless of how she became one, she was considered to be a slut and disgusting--rather than regarding her as a young woman who was perhaps kidnapped and raped on a daily basis. Sort of like how, in many areas of the Muslim world, even in advanced areas such as Dubai, a woman who is raped is a criminal and will be jailed for adultery at best, or killed by her family at worst as having betrayed their honor. Indeed, right wing apologists in Japan still regard comfort women as disgusting, lying whores whose seeking for economic redress today is just another form of prostitution. Check out this video: https://www.youtube.com/watch?v=HrNqBV6Rxkk Please understand the context--these are right-wing extremists, not the general public, who are making these claims. You'll note that a key point of these right-wing imperial apologists is that the women (many were girls, age 12 or even younger) were sold into prostitution by a parent. As if the Japanese military buying a 12 year old and enslaving her into having sex with 20+ men per day was somehow OK if they gave her parent money. Which in most cases isn't true, anyway--many girls were grabbed off the street or coerced in some way.

The point is that a Japanese person in 1940 wouldn't even have a framework to use to see the situation as wrong. They would understand that it sucked to be a prostitute, but that was just the way of the world, they would think, just as it was men's duty to be forced to join the military and fight far away from home. People in Japan had been oppressed by a terrifying and powerful dictatorship for decades by that point. Our understanding today of the mindset of people living in those circumstances, like in Stalinist Russia or modern day North Korea, is that they're unable to articulate the words to complain or protest. They can't think in those terms, having never been allowed to. Certainly now, if you stop someone in the street in Japan and ask those questions, most would be strongly against it and horrified at how wrong it was. But ask someone in 1940, and they first of all wouldn't want to say anything critical of the Emperor or the military because they could be killed for doing so. Second, they would be fully indoctrinated, most likely, in agreeing with whatever logic was given to them about how to think.

Everybody did it, including the allies.