1. If God says something, then that's good enough. God doesn't have to give me his reasons.
2. It is possible for God to make a completely arbitrary ruling - like on which particular animals are clean and unclean. That's his prerogative.
3. I might think I know God's reasons, but sometimes I'll just be guessing.
4. You might think you know God's reasons, but sometimes you'll just be guessing.
5. We can trust God. He has promised us good and has a history of keeping his promises and working for our good.