You'd (and i'd) think it would be from a testosterone standpoint, but in actual practice and experience no matter how the un-neutered male behaves every neutered male keys in on them. The added likelihood of any unfixed male dog running off when any bitch goes into heat has innumerable possible health/financial repercussions... that i personally have incurred in the past.I've always understood it to be the opposite. That it's intact males that are more aggressive towards other dogs. Higher levels of testosterone equates to more dominant behavior. Neutered dogs usually mellow out due to the decrease in testosterone production after being neutered.