I couldn't date someone who was currently (or in the recent past) doing porn. The main reasons are probably that I'm not interested in the overall lifestyle, although I suppose the "lifestyle" might not be all that different than others imbedded in the entertainment and even night club businesses. I'd expect these people would just have a different idea of what's a fun way to spend their free time than me, and would be around too much sex and drugs and partying to have a good understanding of what's "normal" to me.
The next main reason is that I'd be grossed out at the thought of him having sec with others. I don't like to share. I wouldn't be jealous as much as just totally turned off and disgusted at the thought of what he did all day.
However, if a guy was a porn star when he was 18, but turned his life around and was living a mainstream life totally separate from that, I could come to terms with that. Everyone has a past. Stupid decisions someone made when they were young are ok with me, as long as the person has clearly gotten past it.