I do not recognize that translation Wolfgang. Shouldn't it be "Shall die" or "let them die" rather than "Must be put to death?"

But even so, the context of Mark 7 clearly shows that Jesus is pointing out the hypocrisy of the Pharisees, he is not telling them to go out a kill those who openly disagree with their mothers. He is telling them to lay off his people for such a minor thing while they let more clear and blatant sins go unpunished. To me this is a major implication of Christ's message, one that is often ignored by those most loudly professing to follow him.

Do you recall "let he who is without sin cast the first stone"? Do you believe that he meant that mercy only apply to harlots? It applies to all sinners. Christians forgive. They do not mete out punishment. Punishment is the purview of government.