I don't believe the GP disagrees that losing 50% of species is loss of biodiversity. But the OP might give the impression that is about losing 50% of animals, w

I don't believe the GP disagrees that losing 50% of species is loss of biodiversity. But the OP might give the impression that is about losing 50% of animals, which seems more apocalyptic. "What incentives do scientists have to lie about this?" They might believe they are lying "in good faith". Exagerating the impact so people take action. Basically treating the rest of the world as children. And this, like the GP, I too consider counter productive. And a possible answer to "why is everyone so skeptical...". Because scientists (if taken as a homogenous group) are lying to us (as a group of lay people) for some time. Sometimes this lies are just exagerations made with good intentions, sometimes from bribed "scientists" like the ones who defended the tobacco industry, sometimes the scientists were just wrong but acted like they were 100% certain of their results (not technically a lie, but has the same impact on general population).