I think this isn't fair. The article said it was their car that was damaged, and they are lucky that it was not physical to themselves. But nobody deserves to be attacked...yes this is crazy, but I wouldn't harm these people for it.
The article talks about Genetic Sexual Attraction. I have heard of this before, but I think it's only okay if they didn't know they were related. Like sometimes brother and sister are separated at birth, and they meet and fall in love like any other couple. Then they find out they are related...that's not their fault, they were in love before they knew. But with this situation, they knew each other...maybe they weren't bonded (the article says) but they still knew each other as father and daughter. That's what's not okay to me.
If it happens because you don't know, I don't think it's that horrible...sad and unfortunate but not gross. If you do know, well...that's a different story.