Can't the argument be made that if you are a startup and have launched a product to test the market, it would take up too much developer time to think about https? Depending on the nature of the service, shouldn't you defer the extra effort until only after you've validated the product/market fit?
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...
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.
I actually did it last night, from yum install httpd to (self-signed) SSL in less than 15 minutes. There are some webapp considerations, but they are negligible when compared to other security efforts like XSS diligence.