This film proposes premeditated murder, by the Manson crew, instead of a random act of savageness. I think the only reason critics panned this film, is in the hope some of the murderers will be released.
Hillary Duff is 32, and Sharon Tate was only 26.
Another thing that put off critics was the public reminder of how brutal these murders were - and how things could have been different - if only they had some personal protection.
This film has a conservative message that the media functionaries don't like.