Why isn't the extension enabled on all websites by default?

[FelixFourcolor]

I'm intrigued by the fact that you have to manually enable the extension on specific websites, instead of it just working for all websites out of the box. I ended up just having one pattern .* so that everything is enabled and I don't have to worry about it again.

Am I doing something wrong? Are there security/performance/etc. reasons why enabling everything by default is not a good idea?

I saw the wiki mention that this change was made in v.2, but it doesn't say why. It seems like a regression to me. I almost uninstalled because I thought it didn't work.