The Manson murders were "just news?" Can't say I agree with your assessment, frono.
To be fair it made a splash at the time but even the LAPD didn't realize there was a connection between the Tate and LaBianca murders, even ignored tips that may have caused them to connect 'em more quickly.
And Sharon Tate wasn't really THAT big, but the marriage to Polanski also made her newsworthy.
The news faded relatively quickly since the case went cold quickly and wasn't back in the news in til December, and REALLY dominated news once the trial began in '70 and Manson and his followers' antics got them exactly what they wanted:
Publicity.
In my memory, coverage of Chappaquiddick actually lasted longer as a news story than the Tate-LaBianca murders, but the Tate LaBianca murders "came back" and might have been the first time we saw cult leader at work, that we knew of.. but did it
affect history?
I don't really think so, and I think that's all that Frono meant by "just news".
Chappaquiddick probably qualifies as a bigger life-changing event even though far less remembered today.
Who knows what may have become of Teddy Kennedy and the US if he hadn't been permanently handicapped by that skeleton in the closet for the remainder of his career.
I don't disagree with you basic proposition that these were newsworthy events in counterpoint to the "Happy Accomplishments", but I suspect it's just human nature to want to celebrate the anniversaries of good news instead of bad, right?
And hey, how about Altamont?