"The owners of flattr also own thepiratebay. I remember hearing a speech a few months ago talking about how everything should be free, just like when we were children (we need to learn to share). They have no regard for the rights of developers and have no problems giving a clear and direct roadmap to a free copy of your commercial application."

[Citation Needed]

"why does Flattr charge a 10% surcharge on top of every transaction"

Bandwidth isn't free.

"I might use them if they didn't make a profit"

How do you know they are profitable?