I hear this often from dog owners. While it is true your dog is very social, the dog itself is a deterrent to breaking into your house. The dog is even more of a deterrent if the dog is in the house. A barking dog is now aware something is wrong, and is alerting all around of the situation. The person breaking in is unaware if the dog is Snoopy or Cujo and the chance is just too great to take.
Small dogs are great alert dogs.
They will gladly bark loudly to let everyone know that someone strange is at the door. A bite from any dog is not something that a burglar is looking for. If a dog bites someone, the burglar leaves behind far too much evidence. It was only a few months ago in Florida that a Miniature Poodle weighing five pounds scared off a burglar. His owner, a single woman, was in bed reading.