Well, the contradictory argument can be made as well: If you're a start-up, and your early adopters get annoyed because someone made sure Firesheep works with your web site, and they're all getting pranked, they're going to decide they won't bother.
OTOH, I am writing this comment on an open wireless router.
On the gripping hand, nothing I put here is private, and if someone "pranks" me, I can just login again and delete offensive content. Karma isn't actually money...
Your local network admin, your ISP, any ad networks your ISP has or will have arrangements with and your government can log all the websites you visit and build profiles of you because https isn't used everywhere.
This might not bother you individually, today. But maybe it will cause problems for you in the future if laws change? Maybe it is causing problems for a lot of people who aren't you today? Maybe it is causing problems for citizens in countries other than yours?
The World would be better off if https was used everywhere.
OTOH, I am writing this comment on an open wireless router.
On the gripping hand, nothing I put here is private, and if someone "pranks" me, I can just login again and delete offensive content. Karma isn't actually money...