Dude ew, you guys r what's wrong with the world encouraging dis
Fiction and reality are two different things. No one encourages anything - especially reading this. It's a crappy plot for sure, but it's still fiction. So long as people don't replicate it in reality, let people read what they want. I also don't say "ew" to beastiality (and there are plenty of them in novel format) despite not being a fan of it and finding it questionable. But I don't reprimand people for what they read because it's their choice.
Again, people can consume any type of media they want so long as they know what's morally right. There are also worse stories or media which involve pedophilia and such. And historically, incest was very common all over the world and is still viewed as normal for some nations.
Everyone who complains it to be stepcest just goes to show that y'all don't read summaries. Drop it if you don't like it. Easy as that.