Amen.
I just do not understand why people must insist that their is some secretive or special reason why Banner gets angry. Haven't any of these people ever met or know someone who has a short fuse? Ever heard of road rage? People everywhere around the world every single day get pissed off. It's a fact of life. Did everyone who's ever blown up at a co-worker, stranger or even a friend have some dark secret past that caused it? No. The world is a very stressful place and some people just lose their cool faster than others. What the hell is so hard to understand about that?
I have had my share of angry outbursts - and I still do on occasion, but I did not get beaten as a child nor did I secretly witness one of my parents hacking the other up with an axe. That whole back story was garbage. There was absolutely NO reason to "justify" why Bruce Banner gets angry. It's a fact of life. People just get pissed from time to time; and with the world moving at a faster pace every day, and everyone being expected to keep up or fall by the wayside, it's even more stressful. That's just one of the thousands of reasons why there's so much violence in the world.
And let's face it, Bruce Banner gets thrown into situations that would test the stress management skills of Job himself. And lastly, when's the last time you got the crap beaten out of you that didn't fire up your adrenaline levels?

t:
As for why he survived the Gamma exposure? Suspension of disbelief. Every radiation-born superhero would be dead in the real world. Same with all those atomic monsters from the 1950's. We simply accept that Banner has a unique/rare body chemistry that enabled him to absorb the radiation, or that perhaps being a "new" & "unknown" form of radiation (as it pertained to comic readers in 1962), Gamma might do new & unknown things to a person.