While people can avoid a lot of problems with a little common sense, infections don't just come from click happy users. Malware in ads can infect users just for browsing to a site and popular sites like CNN and yahoo have infected users in the past that way. I've managed to convince most of my family and friends to install ad-blockers but some of them still don't. I've tried to encourage the more tech savvy among them to disable javascript by default as well, but most have not.