So that no indivdual should face arrest or prosecution for defending their home.
The police might say this would open the door to 'mistaken identity' issues. Which if it where not clearly an intruder in the middle of the night then it could be investigated, perfectly acceptable.
But if it was an intruder an 'any force' Law would discourage the criminals and eventually remove a real and percieved threat and give innocent people peace of mind.
Civil Liberties/Civil Defence – Redress the Balance
Please use the above phrase where ever possible to further the point.