Here’s the problem with your concept. Many spammers use a giant array of computers to do their spammings. Many of these are zombie computers, your or your mother’s computer, infected with a virus or trojan which lets the spammer take control and use your computer’s power in the background. And do you know one way how your mother gets this nasty thing installed? She downloads a free fish screen saver, or a fun free poker game, or a search bar for her browser, or a rotating wallpaper display, all of which come with tracking tools and avenues to let other suspicious programs in to your computer.
Many spammers only exist because they have a botnet of power to send their emails. If everyone who was in this botnet reformatted and kept their systems clean, spammers would have to resort to using their own resources to spam, and this is much more easily detected and dealt with by anti-spammers.
So by your logic, we should really be punishing the people who don’t know better than to not download a free program.
Or maybe, just maybe, we shouldn’t bother punishing people (punishing people on the Internet is pretty hard, what with the whole “global laws don’t exist” thing), but focus our efforts on educating people on why they should not click on popups and install programs simply because they were “told to do so by the computer”. We can also educate people about how spam pharmacies are not monitored or enforced and thus you have no guarantee that the “medicine” you ordered is what you were shipped – some people have dissected pills bought from spam pharmacies and found them to be a mixture of crap ingredients. Or, and this is depressing to have to say, people need to be informed that there is NEVER a Samoan/Austrian/Whereverian Prince needing to smuggle out millions of dollars, but there IS a Nigerian/Whereverian scammer trying to trick you. Education, not punishment, is the key here.