I'll tell you why it's bad....
there are many people who have overstayed, foolishly, and have no excuse. Many of these people are married to UK nationals, many of them have children. Now, even if they do the right thing and leave the UK voluntarily, they will be barred from returning for 12 months. What would any of you mothers do if this was you? My guess is that many will just keep their heads down and hide from the authorities rather than be seperated from their children.
I believe this will just make the situation worse. Fair enough to do it for those who breach the rules from now on, but there should be some sort of amnesty for those already here.
Vicky