Europe's open borders policy is a stupid idea without a doubt.
I'm a firm believer that anyone who travels through a country deemed a safe haven should lose their refugee status and should be treated as immigrants with no special privileges.
As for who they let in, young Muslim males can still be part of families and children under Abbott's focus.
You are correct, if you reduce the intake numbers, the number of crimes committed would lessen, (but there would still be crimes committed).
Abbott reducing the intake numbers does not prevent the rapes and assaults, it just lessens the amount of them.
Note: The 15 year old gunman who took Curtis Cheng's life was from a family unit who would fit into Abbott's 12,000 criteria.