The state is generally obligated to provide security to homeowners who can not be bothered to lock their homes.
If someone enters your house without your permission and refuses to leave you may call the police. If there are any immediate threats to person or property the police response will usually be swift (though, of course, this depends on your local P.D.).
You have a security problem. You call the police. Now you have two security problems.
I'll stipulate that this isn't what we were taught in junior high civics, but it is the experience of many communities in the USA that security problems are best handled without the intervention of police.
If someone enters your house without your permission and refuses to leave you may call the police. If there are any immediate threats to person or property the police response will usually be swift (though, of course, this depends on your local P.D.).