Yes. I think there are two thoughts and both of them have some truth, but both of them are wrong.
The"Bernie is leading by 5, 10 points and beats Hillary in the GE" is ridiculous. There is an enormous amount of negative attention on Hillary and Bernie has barely hit anywhere close to the scrutiny that he will face under the General Election spotlight.
But Hillary Supporters and Republicans that say "Bernie is a socialist and cannot win" are apparently not paying attention to this election. This election is the Race against the Establishment, and the poll numbers show it. Looking at the poll numbers Americans are warming up to socialism, and the thing is BERNIE ISN'T EVEN A SOCIALIST. I would have preferred him running under the Social Democrat label but y'know it's about damn time we understood what these labels are so I'm glad he did it for that reason.
I think it would be close, but can he win? Will he? That's for the voters to decide.
Bernie Sanders would be the first to disagree with you. He himself is a card carrying socialist and will be the first to tell you. If he weren't a socialist, he'd be in the single digits against Hillary Clinton anyways. There's no way someone with his age and charisma could do better without going to such extreme. As for poll numbers, let's talk about actual votes. This is the difference between our parties. You people like poll numbers, we like votes. What percentage of the country is actually voting for Bernie Sanders right now? Less than half of the Democratic party! This accounts for less than a third of the country! This doesn't win an election.