Although I commend Sanders on running against HRC with an essentially smear-free campaign, it is important to understand that the case would be very different in a general election with HRC as the nominee.
Have you seen full-on negative ads from Bernie about how HRC condemns six month old (mostly Black) babies as super-predators? What about condemning Central American youth to die in order to "send a message"? Have you seen him harp on the multiple government investigations of HRC? How about a litany of measures passed in the Bill Clinton era that disproportionately affected AA and Latin@ folks adversely?
No, you have not. This is a clean campaign ... from Bernie.
HRC has survived earlier Republican attempts to smear her by -- to her credit -- being the bigger person. But she has not been the bigger person in the primaries. Not with the debate schedule; not with the comments from Bill and Chelsea; not with the imagined wedge between Sanders and Obama; not with her attempts to claim foreign policy expertise after voting for the Iraq war and taking advice from Henry Kissinger; not with the ludicrous assertion that her acceptance of Wall Street money is devoid of quid pro quo chicanery; not with ...
But the Republicans wouldn't be so kind to HRC.
Moreover, HRC supporters will vote for Bernie in the general election; many Bernie supports won't vote for HRC, and may choose to vote for a third party candidate or not at all.
And if Trump is the Republican nominee? Then much of the architecture created as a part of the current Grassroots movement -- to position HRC as a marionette with big money groups pulling the strings -- will be easily re-purposed by a self-funding candidate like Trump. And Trump will destroy HRC (unfairly, IMO) on her husband's record; will destroy her on foreign policy by (e.g.) claiming that the Iran deal was terrible, and by noting his own opposition to the Iraq war and consistent support of the vets; will destroy HRC by diverting votes from angry Americans using his own form of scare-mongering and demagoguery; and will destroy HRC for being dishonest, disingenuous, and unlikable.
None of which happens in a match-up with Bernie: In that case, what we have is someone who not only absorbs votes that went to HRC during the primary tremendously well, but also a Democratic candidate who takes votes away from Trump.