That doesn't also go against homosexuality. Just as there is no argument for homosexuals that also is for incest. Now granted I disagree with both, but think about it. "Just let them love who they want it doesn't affect you"
"It's their choice"
[spoiler]Food for thought[/spoiler]
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I'm not trying to argue for more incest here, but tbh it strikes me as kind of backwards that it's actually illegal. It's literally the only circumstance where sex between consenting adults is still against the law.