Horny is as horny does.
I try to act as if we're both positive, but I know I'm negative. I also know I don't have herpes, gonorrhea, chlamydia, and/or any other kind of STD. I'm happy to open up this discussion with any sex partner, and I'm perfectly willing to share my results with them. (My gay doctor also provides copies.)
The first time I talked about health risks with a sex partner (back in the 80's) was awkward for me. But the conversation surprised me because it went so much better than I ever expected. That sex partner was thrilled, relieved that I brought it up. And we proceeded to have the most intimate, loving conversation, that actually made the sex so much more tender and fun. Now, I don't hesitate to bring the subject up (at the right time), and the results have always served me well.
Of course there's no way to know the absolute truth. Sex with anyone exposes you to certain risks. But if you engage in discussions about health before sex, you stand a chance to reveal the mind and personality of your sex partner in a way no other conversation can offer.
This window into someone's soul does not encourage me to engage in unsafe sex, but it does offer a unique insight that can (and does) enhance the safe-sex intimate experience.