I don't think anyone is seriously suggesting we should just give Hillary the nomination. I think it will be good for her and the party if Sanders gives her a tough primary campaign because she'll need to be sharp for the general election. When it comes to Sanders, look, I like the guy but I plan on supporting Hillary through the primaries and here's why (among other reasons):
This is a precarious time in American politics, especially for the Republican Party. I don't think I'm exaggerating when I say if Republicans lose this general election, they could go on to lose the next handful of national elections unless they do something drastic. Either Republicans realize they're slowly losing the center of the political spectrum or they can keep gravitating to the fringe right as they have. If they continue the latter, I honestly think there could be a schism in the Republican Party in 10-20 years between moderates and the Tea Party.
As a Democrat I feel the need to recognize the broad political landscape, that for right now the American center is leaning toward the Democratic Party. Despite every crazy thing Republican Party leaders have said or done in recent years, there is somehow still a significant chunk of our population that thinks someone like Donald Trump or Ted Cruz should be president. That scares the shit out of me and it should scare you, too. And I do think there is an odd double-standard when it comes to what Democrats are allowed to say vs. Republicans. For example, imagine a Democratic candidate for president saying what Trump said about POWs. Their candidacy and maybe their entire political career would be over in a heartbeat. But when Trump says something incredibly offensive about Mexicans? He surges in Republican polls.
Call me cynical if you want, but the fact that according to so many polls Bernie Sanders has a significantly larger chance than Hillary of actually losing to these Republican candidates is a big fucking deal for me. The possibility of a Republican president is simply unacceptable to me given the current state of their party. I consider myself very liberal/progressive, and a lot of what Bernie says resonates with me. Still, he just pushes too many liberal buttons and I have a strong feeling the center of the electorate won't be as accepting of him being a self-acclaimed socialist as the Reddit echo chamber. Democrats cannot afford to lose the center right now because the consequences of the alternative are just too high.
TL;DR - This is not a good time for Democrats to even appear "too far left" with Bernie as their nominee when there are still enough undecideds that could go Republican, and the idea of a Republican president scares the fuck out of me. Hillary is not perfect but she's probably one of the most qualified for the presidency of any candidate in recent history and she's palatable enough for centrists.