[chc]

They're putting it on the Web. Traditionally, there is assumed to be a certain degree of permission involved in putting content on the Web unless you specifically indicate otherwise. If we don't assume this permission, Web browsers would be just as bad, since they download and cache your copyrighted content.

(Note to downvoters: If you believe I'm wrong, a response would do a better job of correcting the misinformation. If you believe I'm posting this is bad faith, you're mistaken. I really don't see how the Web can coexist with the assumption "A program may not download resources offered by a webserver without explicit opt-in permission.")

[TeMPOraL]

I completely agree with you. Opt-in means nothing would ever be done in this world, because everyone would be wasting resources on getting permissions. No browsers, no search engines, no Wikipedia, no HN, no nothing.

The rule of thumb should be: you opt-in when you put your stuff on the Internet.