It's very dangerous, but I think "most serious practitioners die sooner or later" is an exaggeration. The number I see is 1 death per 500 jumps, which I assume is also biased towards people with less experience.
It might have been true for the pioneers of the sport though.
I (and probably the commenter you're replying to) meant wingsuit BASE jumping, who is considered one of the most dangerous sports in the world. I think it's borderline suicide. I think its practitioners are thrill seekers who want a higher and higher rush, much like an addiction, which has a high chance of killing them.
It's more dangerous than jumping from a plane with a wingsuit.