You should read up on The Castle Doctrine/Law.It addresses your concerns and many States have passed it.
"The castle law says the use of force or deadly force is presumed to be reasonable if someone unlawfully and with force enters an occupied home, business or car. Further, if the force used against the intruder was reasonable according to the statute,
the occupant is immune from civil liability for injuries or death."
http://loneranger2008.wordpress.com/...stle-doctrine/