The point of the woman in adultery issue with Jesus was not to say capital punishment can only be done by someone sinless. They were trying to trap Jesus. If He said stone her, where was His mercy, this healing man of God? Also they would appear to be right if Jesus agreed with them, upping their power. If He said Don’t stone her, He’d be going against clear law of Leviticus. So instead He gave an answer that didn’t entrap Him they were not expecting and had no response for.
The Pharisees were hell-bent in trying to catch Jesus in logical pretzels. Remember the whole taxes question? If Jesus said ‘pay taxes’ then he was putting the state before God, if He said honor God, they’d say he was telling people to break Roman law. He said whose coin is it, they said Caesars, and He said “Then give unto Caesar what it Caesar’s and give unto God what is God’s.”
Begin under grace does not magically get rid of severe temporal consequences.
“Being” not “begin”
But your interpretation of this incident, is that Jesus really wasn't teaching standards at all? He just gave a weasel-worded comment to get himself out of a politically dicey situation, rather than give a clear teaching showing the more perfect expression of the will of God?
Can't say I'd buy that.