My feelings: Do not ban any content, ever. Only delete things after they are submitted if they are off topic or ridiculously stupid.
Instead ban the users who vote those stupid things up, or diminish their voting "worth".
Sometimes, I like reading Valleywag stuff. It's certainly on topic, even if it's linkbait or pure lies. It's the comic, tabloid, side of the industry we're in. Maybe you can add a tag that says "tabloid" next to the Valleywag domain instead of downright banning it.
This is a pretty good article from Valleywag:
Why would you want to censor that?
If you have to ask about being accused of censorship, something is seriously wrong. Also, using a poll like this is extremely ineffective. The mob is, as a whole, foolish. I imagine a ton of people are clicking "yes" simply due to a negative reaction to Valleywag, rather than understanding that censoring Valleywag may start a trend here that could get out of hand...
By generally, I agree, banning Valleywag is a slippery slope, or, at least, it doesn't help to solve the broader problems of social news this site faces.