Mine are a free range flock, so it might make a difference when there isn't competition for space, territory or food. Any chicken can avoid another one and the food is for the taking out on the green, so they aren't really in each others faces at all except at feeding time.
I also cull for disposition in my flocks, so all the naturally mean birds have been killed and eaten. That leaves behind those that brook no nonsense but don't go looking for trouble...I call it firm but kind. I like that kind of chicken. I hate a bully and won't feed one.
I guess it has a lot to do with the environment and the flock development whether you have integration problems. I've never had any bird on bird violence that wasn't supposed to happen...like young rooster challenging an older one for flock supremacy. Even then, there has never been blood drawn on any of my adult chickens in their pecking order issues. I've integrated birds quite a bit over the years and never saw any unusual aggression/violence towards the new birds or new chicks.
I think chickens will go as far as you let them and I've just never condoned a bully flock of birds. I've always had multiple breeds in the flock, so it's usually not breed specific, though I've noticed that all the Wyandottes I've ever had were culled for needless aggression towards other birds and to me.