I have no issue. i've seen plenty that are just fine. Good temperament for it, clear heads, good drive. I will say it's always been more prey drive based than bringing out real aggression. Terriers of any sort in the mode of real aggression no matter what is bringing it out, aren't really that controllable.
I myself don't have one because on the off chance that something goes catastrophically wrong and someone gets bitten or hurt GSD's are still viewed as police and Military dogs. If I had a bully breed, anyone and everyone would be after me with relentless fervor. I don't mind the heat, but I don't want that kind of heat
Rather that being viewed as someone that trains police dogs, I'd be lumped with drug dealers and trying to train the killers of babies everywhere. If my sports of choice change some day, i will probably have a bully of some sort of mix that I do other stuff with. I do like strong, agile, loyal and smart dogs. They fit the bill.