How were they (the Beatles) a problem?
The Beatles were the first superstar pop group to simply cease to exist except on record. As late as the 1940s, pop music was what bands played when people went out dancing. The records were just what you listened to at home. The Beatles were the first group to realize that pop had become records, and that they never needed to step on a stage again in their lives. That's a huge shift, and [although] I think it would have happened without them, they were the catalysts.
The thing I'm not at all sure would have happened without them is the racial split. American pop music has always been an interaction between black and white musicians — and it's often oversimplified into black musicians creating and white musicians stealing. But black musicians always kept up with what the white musicians were doing, just the way that white musicians tried to keep up with what the black musicians were doing. By 1963, the pop charts really were intensely integrated. Billboard magazine stopped having a separate pop and R&B chart because the two charts were virtually identical. And the Beatles single-handedly re-segregated those charts. The Beatles hit white America like the biggest thing to happen maybe ever, and they hardly hit black America at all.