I know the context of the verse. The Sabbath was a blessing, and still is in my mind. Goodness, I'm working in a framework that is a little difficult for me, because I see things somewhat differently than the rest of Christianity. But look at it this way: God created laws that indeed conformed with mankind's expectations. He worked with the tools he had in the day. He even gave commandments that seem harsh by today's standards, but were the expectation of the day. He was giving his law to a rebellious people (emphasis on people, as in human), through a person (i.e. fallible human). He gave them what they could understand.

My children are young. To make a point clear, sometimes very clear punishment may be affixed. For instance, I say, "Don't run in the road or I will spank you." May seem harsh. Surely when my children are more mature, they will not get a spanking for running in the road, but rather a talking to.

You find for me a culture in 1200 BC that was not harsh in law enforcement. Mankind was immature. God gave commandments and affixed punishments that they would understand. The point of Jesus' higher law was that mankind was mature enough to understand the spirit of the law and not always simply comply with the letter. Punishment too was changed: no longer were people put to death. They instead faced punishments more applicable to a more mature species.