There are many anime that have incestuous theme. For example, OniAi, Eromanga Sensei, Kiss X Sis, Ore no Imouto ga Konnani Kawaii Wake ga Nai, Yosuga no Sora, Saikin, Imouto no Yousu ga Chotto Okashiinda ga and so on.
Why are there so many incestuously suggestive anime? Some of them were even aired on TV, which probably could spoil public morals. Wouldn't people, especially parents, protest?