Surefire, don't take offense. I was just kidding about outlawing Boxers, although it is true that my dog has had bad luck with the breed. Another Boxer attacked my dog because the Boxer's owner was playing with my dog, and the Boxer got jealous. I think there must be bad chemistry between Boxers and Pitbulls.
No biggie, I know you were joking.
I think the tension between the breeds occurs due to both having somewhat dominant traits.
The lines also make a difference IMO. A "pet" line is usually much more easy going than a "working line"--for example the German Shepherds, Rotts and Boxers bred for police work tend to be a lot more "difficult" (for inexperienced handlers) than these same dogs bred for "pet".
I made sure my dog was bred for good temperament, and I took the precautions of obedience training, socialization (with people, and other animals), and also raised him with firm love. I credit the socialization and training for getting the most out of him.