Lets try and use the same strategy of doing a cost - benefit analysis.

PORN.

benefits: getting ones rocks off faster and / or in a more enjoyable way and / or more frequently.

cons: the individuals who participate might be acting out past traumas and hence their ability to 'freely choose' to participate might be limited and / or absent. pornography might serve to reinforce and / or train ones body to respond to sadistic / massochistic themes, abuse of power themes, etc. this can show up both explicitly and implicitly in how one relates to others. pornography might be part of the cause of explicit and implicit attitudes of 'women enjoy being raped' and 'one doesn't need to use a condom' and so forth. it might also contribute towards people sexually abusing others.

AUTOMOBILES.

Pros: people are able to commute large distances in a short amount of time such that they have a greater range of employment opportunities. emergency response teams (police, fire, etc) are able to respond in good time. people who live in isolated areas are able to work / travel to greater regions.

Cons: a number of people are killed due to motor vehicles each year.

if one outlawed motor vehicles then society (as we know it) would fall apart. do you think that the costs of outlawing porn would be comperable to the costs of outlawing motor vehicles?

i think that the costs of outlawing motor vechicles would be significantly greater because i think one benefits a great deal more from motor transportation than one benefits from porn. every individual? of course not, but generally speaking.