... I'm currently watching a TV programme on this topic - it is not something I'm undertaking personally!
Technically, two step-siblings having sex etc is incest.
But the technical argument can be picked apart on one component that seems to vary from continent to continent, culture to culture.
Some say incest defines only blood relatives engaging in sexual activity. Whereas others clarify it as an act of sexual activity between any two close members of a family.
So how do you see it, between step-siblings?
Does the "You can't help who you fall in love with..." cliché apply here?
Or the "Each to their own...", "Behind closed doors..." attitude?
Or do you agree that it's illegal/perverted and should continue to be regarded with contempt?
Personally, I find the idea uncomfortable, probably because, although they're unrelated, there is that attachment of a sibling term. Brother... Sister... And that morphs into lover? Husband? Wife? Heh - it doesn't sit right with me.
That said, since they're not blood-related, I see no real reason why they shouldn't begin a relationship. It isn't inbreeding - their kids would not turn out with mental or physical deficiencies as a result - nor is it harming anyone else. It is really just two strangers being brought together by a different set of circumstances. And I cannot ignore my own morals on being judgemental, so I maintain my personal belief that people can, and will, love who they want.