I would recommend reading or listening to Noam Chomsky’s Understanding Power. It is a compilation of several of his Q and As about his ideas about the US political and media systems. He has a whole book about the media called Manufacturing Consent, but Understanding Power will give you the lowdown.

Essentially, all mainstream US media is beholden to capitalistic (for advertising) or state (for funding) forces, so a person should always be aware that news sources are never going to print something that is against its own interest. Things like LGBTQ rights and right to abortion don’t put news outlets sources of money at risk, so they’re safe to print, but you’d be hard-pressed to find something that challenges, for example, the military industrial complex.

I’m not doing it much justice but that’s a very very general and incomplete jist of why it’s good to be skeptical of the mainstream media in general.