Porn actors get screened far more frequently than any of us do in our private lives. But because they have sex with so many people in a short amount of time, during that window period between when an infection occurs and when it is detected by a test, there is a high risk of spreading it. I highly doubt any of them are unaware of the risks of what they do.
While tragic for those infected, the number of infections is not high enough to be called an "epidemic." And while I can't argue against anyone's choice to take responsibility for protecting themselves, I'm going to be a hypocrite and say I don't want to watch it. It is a huge turn off to see sex in porn with condoms and I will always skip on to the next scene.
Last June, a gay performer tested positive for HIV and had used condoms in all his scenes. Demanding they use condoms on camera will not protect them when they don't use them off camera.