For many people, sex has always been at least a bit dangerous. Sometimes, the risk has been of dying: through the chance of catching syphilis / HIV, or the chance of being discovered and killed (say because the sex has had the death penalty or they'd be lynched), or because of other dangers. For many of them, that hasn't stopped them having the sex.
HIV is something I am interested in, because I am interested in sexual health.
Before HIV infection causes the collapse of the immune system, there aren't any symptoms. This is why people have HIV tests: to know if they have it or not.