Losing 50% of species _is_ the loss of biodiversity by definition. Just about every species plays a vital role in maintaining a habitat and losing 1 or several has consequences that are hard to predict and could mean a drastic reduction in the ability to grow food and have clean water.
What incentives do scientists have to lie about this? Why is everyone so skeptical about warnings that scientists around the world agree on and have been saying for 20 or 30 years? It's maddening
Losing 50% of species sounds bad, but much less bad than losing 50% of all mammal populations. Are we just talking about losing ten thousand obscure rodent species? I actually have no real idea what this value means, which makes me inclined to ignore it. A scientific source would be great, but the article doesn't provide any.
If we're talking about "human extinction" level threats, it would probably be from massive famines, and "half of the animals are now dead" seems much more likely to cause that than "half of animal species are extinct". What is the actual percentage estimate that we would go extinct from this, and when? It matters when comparing it to nuclear war or AI.
The incentive for scientists to lie seems obvious to me. They want people to support and fund their efforts (possibly for noble reasons, possibly because they just want more money). They think that simple facts aren't good enough, so they use fear tactics like "we could face our own extinction" hoping that will convince us instead.
Also, the authors of these articles and the people interviewed are not necessarily the scientists either. Given that sources aren't provided, I have no idea what the scientists are actually saying.
Most animal species are insects, so probably that is the majority of animal species that will die out. Insects and grubs, worms etc though can be very important to the local ecology. Loss of some could damage human food production that relies on them in sometimes very indirect ways.
But insects are also a foundation of natural food webs; we can't lose lots of insects without losing lots of other animals too. And as a couple of us have posted already, a recent study showed that we've reduced the populations of mammals, birds, fish and reptiles by 60% since 1970: https://www.theguardian.com/environment/2018/oct/30/humanity...
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).
What incentives do scientists have to lie about this? Why is everyone so skeptical about warnings that scientists around the world agree on and have been saying for 20 or 30 years? It's maddening