How did we get so casual about conspiracy theories?

I was talking with someone today about nutrition. This person has a PhD in material science. They mentioned eating beef daily and I asked about the cholesterol implications. The answer was about a vague 'they' wanted us to think that, but it wasn't true anymore.

I hear the vague 'they' so frequently now it's just a normal conversation. In truth, as soon as I hear the vague they I dismiss the speaker's credibility on the subject, but how did we get here? Vague they wanted us to think X is a valid counter argument by the most highly educated people in our society?

This sounds like more of a rant than a question, but I do truly want to know how this happened? Was it pop culture like the X Files that made conspiracy theories main stream? Was it social media? When will the vague they stop being an accepted explanation? Has it always been this way and I didn't notice?

Thanks, love you!