I don't think he was right to create only two humans, because then were all created from incest. because God had only created only two humans to reproduce, which means that we all originated from them, making us all related in a way. When I think of that it makes me feel gross.
1. Why does it make you feel "gross"?
2. Why does it matter?
(I think Genesis is very literal)
(to actually answer your question) It didn't matter at the time because Genetic mutations were thousands of times less likely to occur because of how little breeding had occurred.
Let me point out before this goes any further, however. Who are we to judge God's decisions? Where were you? Job 38: 4-7 says "Where were you when I laid the foundation of the earth? Tell me, if you have understanding. Who determined its measurements"surely you know! Or who stretched the line upon it? On what were its bases sunk, or who laid its cornerstone, when the morning stars sang together and all the sons of God shouted for joy?" My favorite quote ever and also a summery (not really) of all of Job 38 and 39 says "This is God"s universe and he does things his way. Now, you may have a better way of doing things, but you don"t have a universe." -J. Vernon McGee
Now we can sit here and speculate all day long, and I'd love to, as long as we keep that in mind.
The question should be, Who are you to say what god did and why? We can question him and we can speculate because the more we wonder the more we realize what life possibly is. And what it could possibly be. We live and we die. Either way you look at it he did only create two people to create the human population. That is my question why only two so we can all become inbred it is the thought that grossed me out. You have to think I am 16 so it would be gross to me to think of inbreeding, wouldn't it have grossed you out?
Look at my profile, I am 15. This doesn't gross me out, other species do it all the time. Also, It wasn't like today where parents have 2 or 3 kids and that it. Adam and Eve had at LEAST ten kids. In a perfect society nothing would "gross anyone out" it was perfect and holy.
I don't look at other people profiles, but the human is far more advanced than other species. Bringing in others species was getting off the topic, the human mind works in various different way I know that animals do it because I have worked at vets office. But animals are not human yes they are alive, but they don't know what we know and how it can affect others.
I feel as though your main argument is that it can negatively effect the children or others, and, as I have stated, it didn't matter because the reason for mutations is the amount of breeding that has occurred thus far, so it wasn't an issue.
Another thing you've said repeatedly is that you are "grossed out" by this. When you think about this I would encourage you to remember that you are thousand times removed from these people, but also not to judge God because he is almighty and just. Either way, whatever he does is right.