Yes, Manchin should run.
(1) Manchin can certainly "grow" in his views on abortion (think Jimmy Carter, Dick Gephardt, Al Gore, Teddy Kennedy or Jesse Jackson), planned parenthood, SSM, etc.
(2) Many Dems, along with Americans generally, are tired of the country being divided on wedge issues.
(3) Many Dems, along with Americans generally, are disillusioned (or worse) with Trump.
(4) It would bring a segment of the population that has been isolated and sometimes vilified in urban-dominated Democratic circles, into the conversation.
Sleazy Manchin has been a frequent apologist for Crooked Trump and has frequently voted for his agenda (or the Congressional Republican agenda.) Hardly any disillusioned Democrat would look to Sleazy Joe to protest Crooked Trump.