I think rivalries are what makes great sports entertainment. Playing your hated rival always makes for a more intense and fun-filled atmosphere.
In most areas of life I'd agree with you wholeheartedly. Not sports, though.
I agree with the above fully. But what I question is the level of hate that is often achieved in some rivalries.
Such as when the Celtic fans once blocked the hotel of the Lakers to prevent the Laker team from attending a practice round before the begining of a championship series. That crossed the line between sportmanship and hate.
I am very much involved in several rivalries:
USC vs. UCLA, USC vs. Notre Dame, Dodgers vs. Giants, Niners vs. Raiders
Of those three, the only one that to me represents what a good sports rivalry should mean is USC vs. Notre Dame. The ND fans are great people who, for he most part, view sports as I do, a friendly rivalry where manners take precedence over the "hate" of an opponents fan. You can "hate" a team, w/o having that hate spill over against their fans.
All teams have their fans that cross the line, it just seems that some teams attract a fan base which can carry things a bit to far (Raider fans for example).