1) that all sounds nice if you ignore the fundamental problems, namely, God did intervene and supposedly knew the consequences of his actions. 2) ...from the story there is no hint Abel would have been murderered without this intervention. 3) ...so why did God intervene and then not stop Abel from being killed, but only show up afterwards...and then be so odd about the punishment.
1) God was not wrong to choose to counsel Cain. Cain (like us) had free will in choosing to listen to God or not...the fault and failure was Cains alone.
2) You could say that or you could say that God 'knew' sin/murder was crouching/waiting for Cain and so He chose to warn him so Cain could avoid a fall if he chose too.
3) Free will, free will, free will...When it come to obeying God or not WE HAVE FREE WILL. The punishment was God's to choose. If you think its odd, thats your right.