On this forum, I see multiple threads about rooster aggression toward people, and am wondering if this is a common problem, or if it's only a minority of roosters who are causing all the fuss.
A lot of different opinions here, a lot of different experiences. That's what I'd expect on any chicken behavioral question. I'll give some of my opinions.
If you read enough posts on this forum you will find Silkies, Orpington, Games, Rocks, Wyandottes, and all other breeds where some roosters are terrors to their hens, to people, or both while other roosters of these breeds are the gentlest and sweetest. Breeds may have general tendencies but I find the personality of the individual to be much more important. For tendencies to mean anything you have to have enough for averages to mean something.
The nature verses nurture debate. How important is each? That debate has been going on forever, not just with roosters. Are some born evil or is it a learned behavior? In my opinion both are important but nature may be more important with some individuals, nurture more important with others. I believe you can shape the personality of your flock by selective breeding, hens as well as roosters. If certain behaviors win them a date with the stew pot then in a few generations you can have a flock that doesn't exhibit those behaviors very often. That doesn't mean you can totally breed it out but you can greatly reduce it. I also believe you can teach certain behaviors. In my opinion I believe nature is stronger in some individuals, in some nurture is stronger.
I believe strain has more to do with this than breed. If a breeder selects the ones that get to breed based on certain personalities and behaviors they will eventually have a flock that exhibits more of the behaviors they want. You cannot totally get rid of certain instincts but you can strengthen some and weaken others.
Many people on this forum form their opinion based on their immature cockerels and pullets behaviors. Things can be pretty wild when pullets and cockerels are going through puberty. The behaviors of mature hens and roosters can be a whole lot different than the behaviors of juveniles. When they mature they tend to calm down but getting through that phase can be really hard. I'm talking about both the behaviors between the boys and girls and the cockerels' behaviors toward humans. I give the cockerels a chance to learn that attacking humans is not good. If they don't learn that really quickly they don't get another chance.
I think our expectations play a part. What I might see as normal chickens behaviors other see as aggression. I don't have much tolerance for human aggression but chickens naturally do things. I remember the lady on here who grabbed her shotgun and blew away a neighbor's free ranging rooster that was "raping" her free ranging hens. The rooster and the hens were just doing what was natural, if you let them free range you should expect that.
I think the way we keep them plays a part. If we keep them penned in a small area where we have a lot of interaction the chances of human aggression goes way up. I think this is especially true if we have kid out there playing. Even if the kids are not chasing the chickens they are running around screaming and can easily look as if they are threatening his hens to the rooster.
As to your basic question, how common is aggression, I don't have a good answer. Some people tend to have a lot more problems than others. To me it is not so much that 30% or 70% will be deemed aggressive, but it's what your rooster does. It's either 0% or 100%. I suggest you pay attention and protect your family.