The short answer is this.
I voted for Bernie. I was impressed most of all by his promise that he would "never be a spoiler." If he goes on attacking Hilary at this point he is a spoiler, and I have no more respect for him. Trump is very real. Trump can sure as hell get elected, and if the Republicans run somebody else, that person will likely be worse than Trump. You think nobody disagrees with you because you don't associate with people people who disagree with you. There are a whole lot of right wing nuts, and there are a lot more people who identify themselves as like Trump, and don't care who he insults.
If Bernie goes on sabotaging the left, he is responsible for the consequences--just as Ralph Nader will always be remembered as the lovely guy who brought us the war in Iraq.