There was no one else to marry, if you think about it. But you have to take into account the newness of the creation at that point. The genetic line was very pure. The prohibition against incest wasn't handed down until Leviticus, when inbreeding became a problem.
"People in the Bible" were as human as the rest of us, and all sinners. Look at David.
The definition of “sin” is, a violation of God’s Law.
During a period of time such as with the very first of God’s Creation, if God did not have a law against procreation by members of the same family, then it was not a sin.
Under different conditions at another time, if God in his Wisdom had a law against such, then it would become sinful at that point to do it.
Again, sin is a violation of God’s law. If no law of God, then no sin.
If a law of God, then violation is sin.
Good answer and very true. If it was only Adam & Eve, and then Cain killed Abel... who else would have procreated if not for siblings, cousins, etc. As you said, the initial genetic line was very pure from the original creation, and God commanded Adam to be fruitful & multiply. By the time Leviticus chapter 20 came along with it’s prohibitions on homosexuality (and equating it with bestiality & incest), there would have been no reason for incest to continue, and in fact was punishable by death.
Don’t get sucked in...these people seem to be mocking Christianity and trying to create arguments.