If you are still on the fence in the Democratic primary, or still persuadable, you should know that Vox interviewed a number of political scientists about the electability of Bernie Sanders, and got responses ranging from warnings about a steep uphill climb to predictions of a McGovern-Nixon style blowout defeat. And all of them dismiss current polls as meaningless.

You are, of course, free to disagree. But you need to carefully explain why you disagree — what evidence do you have suggesting that these scholars’ conclusions, which are based on history and data, not just gut feelings, are wrong?

And there are two really unacceptable answers that I’m sure will pop up again and again in comments. One is to dismiss all such analyses as the product of corruption — they’re all bought and paid for by Wall Street, or looking for a job in a Clinton administration. No, they aren’t. The other is to say that you’re willing to take the chance, because Clinton would be just as bad as a Republican. That’s what Naderites said about Al Gore; how’d that work out?

I have some views of my own, of course, but I’m not a political scientist, man — I just read political scientists and take their work very seriously. What I do bring to this kind of discussion, I hope, is an awareness of two kinds of sin that can corrupt political discussion.

The obvious sin involves actually selling one’s views. And that does happen, of course.

But what happens even more, in my experience, is an intellectual sin whose effects can be just as bad: self-indulgence. By this I mean believing things, and advocating for policies, because you like the story rather than because you have any good evidence that it’s true. I’ve spent a lot of time over the years going after this sort of thing on the right, where things like the claim that Barney Frank somehow caused the financial crisis so often prevail in the teeth of overwhelming evidence. But it can happen on the left, too — which is why, for example, I’m still very cautious about claims that inequality is bad for growth.

On electability, by all means consider the evidence and reach your own conclusions. But do consider the evidence — don’t decide what you want to believe and then make up justifications. The stakes are too high for that, and history will not forgive you.