Users' choice between opt-in and opt-out should be made systemwide, imo. There should be an option to enforce the wish not to have any software installed on the computer (without the user being asked first).

There's a lot on this and nuclear risks in general in Bernard Cohen's book "The Nuclear Energy Option" which is available online at: http://www.phyast.pitt.edu/~blc/book/index.html If you only read one chapter, make it Chapter 11 "Hazards of High Level Radioactive Waste - The Great Myth". You should at least find it interesting!