Aggression can and does have a genetic trait. Notice I said "production strains" not breed. RIR and leghorns have many production strains. Especially leghorns. One nasty strain does not mean ALL production strains are going to be the same.
There is a strain in particular, where the majority or all roosters become extremely aggressive and actually deliberately kill hens if they have access to a hen. (This strain is mentioned in one of Tempe Gradin's books) This is an extreme example but this also is proof that aggression can and does have a genetic basis.
One wonderful example are some fighting game lines, where the roosters will not think of attacking any human(and children can play with like mentioned above) but their desire to absolutely murder another rooster is not lessened in the slightest. Other lines will fight anything, be it birds, dogs or humans. They even have a word for those lines; "manfighters".
There are many completely non-aggressive roosters who certainly breed very vigorously. Just about the only time non-aggressiveness is a disadvantage is if a very mellow rooster is confronted with an aggressive hen who challenges him.. and he won't stand up to her. I've seen such roosters take on a tactic of sneaking up and catching her by surprise.. sometimes this ends up in the hen accepting him.. eventually.. LOL But this is a good example of disproving that aggression is needed for fertility. Those roosters have low aggression BUT high desire to breed.
Some people like spunkiness.. nothing wrong with that. Also absolutely nothing wrong with culling roosters that go after people.. this actually has a reasonable basis as those roosters CAN throw sons who do the same.