The proliferation of social media platforms has sparked vigorous debate regarding its impact on public discourse. Proponents often laud these digital arenas for democratizing speech, arguing that they empower marginalized voices and facilitate rapid civic mobilization previously hampered by traditional gatekeepers. Indeed, movements advocating for change frequently utilize these tools to organize and disseminate critical information swiftly across geographical boundaries. However, this perceived liberation is counterbalanced by significant concerns regarding the echo chamber effect and algorithmic curation. Critics point out that such environments tend to reinforce pre-existing biases, fostering polarization rather than genuine dialogue. Furthermore, the incentive structure of 'likes' often rewards sensationalism over nuance, leading to a decline in reasoned debate. Thus, while social media undeniably enhances connectivity and provides unprecedented platforms for expression, its current architecture simultaneously risks fracturing shared understanding by prioritizing engagement metrics over substantive discourse. According to the passage, what is the author's central argument regarding social media's influence on public discourse?