Disabling features with Javascript? I bet it's easy to write a Greasemonkey script that'll give you the paid features on all these sites.
"Only a very, very small minority of users would ever attempt to do something like this, and worrying about these users is a waste of your time and your money. There will always be those people who will do literally anything they can to get around paying for something."
We really do think worrying about these users is a waste of your time though. Just like blocking ads, if you want to try to get something for nothing, you can.
Lastly, sites don't even have to enable any of the premium features. They are optional. Contenture is as much about users supporting sites that they enjoy as it is about enabling premium features on your site. Because everyone knows ads don't even pay the hosting bill. If you don't want to pay - that's your decision.