Leaving your computer off and never using it is 100% effective against computer viruses, Trojan horses, and hardware failure. It is the ONLY 100% effective measure, and therefore, by your own logic, the only measure worth using. So if I catch any of you using a computer, your abstinence-only argument is worthless.
There are, however, some abstinence-only advocates who actually DON'T use computers, particularly since it's a religious movement, and some religions disdain many forms of technology. For their sake, we can construct a similar argument regarding food poisoning. Knowing how to recognize harmful foods and spoiled foods would go against their creed, as the only way to prevent food poisoning is to stop eating. Sure, people need to eat. People also need sex, or some substitute that the abstinence-only people think is immoral. I think that highlights the importance of knowing how it can be done safely, when it needs to be done.