Why do gospel contradictions matter?

[Brakeman]

First off, I'm not a believer. But I constantly hear from fellow non believers that the gospels aren't reliable because they contain contradictions. Honestly, I don't understand why this argument is used. From my understanding, the gospels spread by word of mouth for at least 20+ years before being written down.

It matters most because the authors of the gospel versions we have claim that they are divinely inspired and proofread by the holy spirit.

If they contain errors they could not be divinely inspired by a perfect god and thus could not be god's word, but instead would be man's word, and men lie like shit!