Any objective look at the realities of the two candidates and what they each are up against in the general election bears this out:

Sanders attracts Independents, the largest demographic, and he attracts some Republicans. This matters in the general.

Closed primaries didn't allow Bernie to demonstrate his strength among all voter.

The support Clinton got in the South is meaningless in the general, red states go red in November.

Bernie has no baggage, very few negatives, and polls show him consistently kicking ass over the GOP.

We are royally fucking ourselves if we nominate the weaker candidate.

...and America is creating disaffected nominee at a record pace. Even the chance to elect the first woman to the presidency may seem less important to youth facing economic apartheid.

Won't have their vote counted.