The Law vs Grace in God, With Skin On

In biblical times, adultery was punishable by death. That was the law. And yet David not only commits adultery, but he also has Bathsheba’s husband killed. Where is the justice here? David should have been stoned to death! Just like the woman who was brought to Jesus whom they found in the very act of adultery. But then I always wondered, Why bring the woman, what about the man?
And then there was Grace. The dispensation ushered in by the resurrection of Jesus Christ and continues today. Which begs me to ask, is that being fair to those who lived before that time? It also makes me glad I didn’t live back then. Let’s just say, I would have been stoned. Not for adultery, but for breaking some of the other laws.
I think sometimes we use Grace as a crutch or excuse to do what we know is wrong. After all, it is easier to ask for forgiveness than permission, especially when we know permission would not be granted. Can those who lived before Grace cry foul? How unlucky to have been born 100 years before Christ.