Why would you even think of having sex with your sister in the first place? If sex is what you want,you can just go get yourself a girlfriend.
Or did you fall in love with your sister?Your mother is your mother,not lover. Your sister is your sister,not lover. Your pet is your pet,not lover. I feel dishonoring brother-sister relationship if I ever consider incest.
I've a sister and despite how close we are and we've been living in the same house for so many years,I never fall in love with her.
Incest=No children=Extinction of human being