I believe you'll find, if you check the comparatives and forums, that there are a few free AVs that are well worth having. There are also a few premium AVs (paid) that you might not use, even if they were free. Just my two cents.
Stand alone anti virus products (free or paid) have been proven to be as little as 28% affective against new threats. As a stand alone solutions they are no good. I really don't see the point in even using anti virus if there is such a great chance of missing highly dangerous threats. Good protection comes when you combined a traditional anti virus engine, a cloud, strong hips, solid firewall, behaviour blocker, and even a sandbox. Maybe then you stand half a chance of stopping malware. Products with this level of technology require a lot of development, and money.
I suppose there are free applications which will do all these things but the average joe doesn't want to be missing around with 7+ free different applications and keeping up to date the latest software when you can install one suite and have done. Comodo IS is the only free security software I would use but I don't think it will be too long before free becomes $25 a year.