The personal cannot be separated from the common, the community is itself a collection of individuals. The common good is not only pertaining to happenings in public spaces. People who mistreat themselves and others privately still pertains to the common good, eating unsafe food in private will still degrade society and healthy foods should be encouraged (this has not been done in the United States, I've heard it's better elsewhere but I can't be certain).
We could say drug addiction is a "personal" evil, it should still be combatted (I oppose [most] drug advertising for this reason). I've known people who harmed their bodies, irreparably in some cases, without harming anyone else. But that's not the whole story. Their family relations are degraded, they cost public resources, they have worse relations, and not to be forgotten is that they are people who deserve love, help, and support. I apply this to other evils other than drugs, such as pornography.
Pornography is sold, provided, promoted to the general populace. It has an affect on real people and is typically spread socially. Discouraging and disrupting this helps individuals and groups by helping discourage immoral and unhealthy actions from spreading. Pornography affects an individuals outlook on not only themselves, changing their own view of their sexuality, but also changes how they view others, this is especially important in children who are developing in so many different ways.