Obviously the pervert friends finding happiness with a sex worker is setup for ichikawa's reaction. Because after kanzaki does it she will notice something really weird going on with her friends. The perverted talk does down, they stop buy porn, they stop mention how much they want to get laid entirely because they have. Then finally she confronts him about it and he says "I gave them what they wanted, how is that a bad thing?" And she wont be able to reply because she knows that really is exactly what they have always wanted.