You mean everyone here? Pretty elitist there, also considering that no one here has a PHD...
A PhD doesn't make someone an expert. Expertise comes from qualification
and experience in the field you're studying.
And I don't think Headcrab's trying to claim that anyone here is an expert. But the difference between the posts that Headcrab Zombie and SeventhSandwich make and most everyone else in this topic, is that they're backed up with sources from credible journals and meta-studies, done by credible expert doctors and professors, who all publish their findings and their work, so that other credible scientists can cross-examine it.
They're not debating their opinions, they're expressing the results that are supported by countless credible experts from across the globe.
And even should none of us be experts, there are plenty members of this community who have a clear passion and understanding for science, combined with varying qualifications in those fields, and take an active interest in learning and studying these sciences.