Consider this conversation happening over at Sam Ruby's weblog. The fundamental question comes down to whether or not modifying the content of a web page is an OK thing to do. Microsoft's SmartLinks technology and Google's toolbar thingy represent the act of a corporate entity imposing modifications on content created and owned by others. The Firefox Greasemonkey plugin represents the act of an end user modifying the content being viewed. There is lots of controversy about both. Are SmartLinks, Google toolbar things and Greasemonkey stuff "evil"? Well, let's consider it from a different point of view in a different context.
If I buy a book from Amazon. If, when I receive that book, I open it up and find that someone from Amazon went through and scribbled a bunch of stuff in the margins (e.g. references to other books, ads for other products available through Amazon, etc) I would be quite ticked and justifiably so. The book publisher and author would also rightfully have something to say about it and Amazon would/should get in trouble for doing such evil things. However, if after receiving the book I decide to scribble notes in the margins, underline passages, rip out pages, etc, that's a perfectly acceptable thing to do. It's not evil.