Evaluating groups based on their goals rather than their methods is a problem. The Far Left wants everyone's needs met, but historically (and even today in places like China) end up putting a bunch of people in camps and gulags to achieve that goal, squashing dissents to meet that goal, and banning the practicing of religions to meet that goal, kill political dissidents to meet that goal.
If the Left wants to win those Centrists they need to assert their belief in individual rights; they need to disavow the Socialists and Communists of the past and present who implemented those horrible things. When you have prominent American leftists like Bernie on record praising Venezuela; praising the USSR etc... it makes them appear equivalent.