simply going "nah, don't believe it" is an instinct that has to be honed with life experience, and one that will eventually get it wrong, so you still need alternative media sources.

You also need a background understanding of how the world works (ie, theory) to replace the propaganda with anything useful. If you don't, you might distrust the propaganda on instinct, but get drawn into a completely bogus explanation for whatever the propaganda is trying to cover up. Which is where I think a lit of reactionary conspiracy thinking comes from.