It is a big deal!! I don't know about you but An 11 year old is still a kid to me.
They shouldn't be exposed to hardcore s*x, ra** scenes and the amount of violence found in this story.
a sm** bl manhwa is not the place to learn about these topics so get outta here !!! With no maturity nor discretion, it's quite easy for a kid to normalise the stuff shown here!! And If you don't find that harmful then you have an issue.