Are you suggesting that you never know if the computer you are buying has windows on it or not?

This is not the same thing at all. These computers all advertise that they come with Windows. It isn't like when you buy it, you have a 5% chance of it being infected with Windows.

If the Cyclospora lettuce was labeled as containing Cyclospora, and you could choose to buy that lettuce or some other lettuce, then yes, it wouldn't be a problem.