People who already lean toward a proposal meet to discuss it. Each contributes reasons in its favor, hears those reasons repeated by others, and leaves more confident than before. The group has deliberated, but the discussion may have narrowed the range of considerations rather than widened it.
Group polarization names the tendency for some discussions to move participants toward a more extreme version of their initial inclination. It is not the claim that every conversation produces extremism or that strong agreement is necessarily mistaken.
More arguments can still mean less variety
If participants draw from similar experience, a long discussion may circulate closely related information. People may also adjust their expressed position to fit what they believe the group respects. These possibilities make the composition and incentives of discussion important.
Inviting different perspectives can broaden the material available, but simply placing opponents together does not guarantee careful listening. Participants need reasons to examine evidence rather than perform loyalty to their side.
The useful question is what changed during the conversation. Did people encounter information that could have challenged their initial view, or mainly discover that others shared it? Confidence after discussion is more informative when the process has allowed meaningful disagreement and tested assumptions, rather than treating agreement itself as proof of sound judgment.