If your blog quotes from and links to my blog, that's an endorsement, and I would probably be happy about it.

But if you print out my blog and sell it on Amazon, I would definitely be pissed off.

Some behavioral economists say that people operate in two modes: A "warm and fuzzy reciprocity" mode used with friends/family/neighbours/colleagues and a "coldly calculating market" mode used whenever there is money involved.

If you collect a few entertaining tweets and publish them on your blog, most people would probably consider it within the spirit of reciprocity - it's a shared resource with no specific owner.

But by selling the collection, you are breaking the implicit social contract that governs reciprocity and switching to market mode. In market mode I will obviously demand my fair share of the profits, and by not offering it you are breaking the social rules for market interaction as well. (See "thief" - exploiting other people's effort for profit and offering nothing in return.)

So yes, selling the book probably generates more anger than giving it away. But it's not much of a mystery why that is so, is it?