Palant said explicitly in a blog post that he turned the whitelist on by default because the vast majority of people don't change the default.
The forum has also been inundated by complaints (I've been following this) from people who installed ABP for 4, 5, 6 of their non-tech savvy friends who don't know what's going on, why ABP stopped working, and how to change it back. Thus, Palant has unwittingly caused (perhaps) hundreds of thousands of people to be inundated with tech support requests from their friends. That's part of the backlash.
I get that, I think here though, the idea is that those defaults are probably fine for the average user that can't be bothered to check the config. (On a tangential note, as that link talks about reinstallation and rote reconfiguration, this would be an example of where unix-style/philosophy is so nice. Configure it once, back up your config files in version control and you're good to go even if you reinstall.)
http://www.codinghorror.com/blog/2007/01/the-power-of-defaul...