its simple really,
the rword instantly makes the revenge inherently sexual. which is weird and doesnt sit right with a lot of people. also its not him alone doing the revenge, he lets the ones which suffered in this world (villagers) also take their revenge. and lastly, we are reading revenge manga and people want to root for the "good" guy. many people had the intrusive thought: "i wanna harm them as revenge" but no one sees r*pe as revenge (in the current time). also people will accept what they want to accept and very few will accept sexual crimes
TLDR: its less worse in fiction