I have a dog that is the most loving, loyal thing I've ever seen but she only weighs about 25lbs (Rat Terrier) she would give her life defending me, but she can only do so much.
We live out in the hills and there have been a number of break- ins and thefts on neighboring properties, having been a victim of crime in the past (truck stolen) that feeling of violation never left me, out in the country there isn't anyone that's going to hear my windows breaking or my little dog barking.
The feeling of security that a more imposing dog brings is comforting when you're away from the house.
As a kid I grew up with German Shepherds and looking at multiple websites including those of insurance companies, Shepherds inflict more documented bites than Dobies, perhaps due to their popularity and sheer numbers, but I never saw any bad traits from our dogs growing up.
I like the looks and athleticism of the Dobermans and the fact that they have a very sleek coat that doesn't shed much.
On the other hand, I don't want a dog that absolutely terrifies every person that comes to visit or that would put kids at risk.
Like most big imposing dog breeds, it seems there are lots of owners that defend their dog of choice endlessly, and those who despise the breed based on their bad experience with it.