Suppose an advanced civilization on the other side of our galaxy observe the Earth at this very moment, they are seeing the early homo sapiens. Suppose they send a radio signal to say "Hello world!", it will be received about 100 000 years later when our civilization will likely be not anymore. The End. Now, if you think about a courtesy visit, it's even worse, odds are the Solar system will be no more by the time they arrive.

The point is incestuous relationships were forbidden because they lead a higher probability of genetic defects in the offspring. They were also forbidden if they are not consensual like any other sexual relationships.

Clearly dating your daughter isn't consensual given the imbalance of power at play. That's also why pedophile relationships are forbidden.

Unless they can reproduce, I don't see the issue here.

Probably another "Japanese" stealthy tactics.