In the original Fallout you could defeat the final boss just by talking to him, but in addition to the speech skill you actually had to find and bring the evidence that his plan was doomed to failure. The issue wasn’t a matter of opinion - you needed scientific proof.

You could also choose to let him convince you that he was right, which was one of the ways to get the bad ending.

Speech, aka mind control.

Destroy them big guy with FACT and LOGIC

Courier: You can east the west but only if you west the east.

Lanius: Fuck, you’re right