The rapid integration of AI writing tools into online platforms raises critical questions about their impact on content production and outcomes. We leverage a unique natural experiment on Change$.$org, a leading social advocacy platform, to causally investigate the effects of an in-platform ''write with AI'' tool. To understand the impact of the AI integration, we collected 1.5 million petitions and employed a difference-in-differences analysis. Our findings reveal that in-platform AI access significantly altered the lexical features of petitions and increased petition homogeneity, but did not improve petition outcomes. We confirmed the results in a separate analysis of repeat petition writers who wrote petitions before and after introduction of the AI tool. The results suggest that while AI writing tools can profoundly reshape online content, their practical utility for improving desired outcomes may be less beneficial than anticipated, and introduce unintended consequences like content homogenization.

翻译：AI写作工具在在线平台上的快速整合引发了关于其对内容生产及结果影响的关键问题。我们利用领先的社会倡导平台Change.org上的一项独特自然实验，因果性地研究了平台内置"AI辅助写作"工具的效果。为理解AI整合的影响，我们收集了150万份请愿书并采用双重差分法进行分析。研究发现，平台内AI访问显著改变了请愿书的词汇特征并增加了请愿同质性，但并未改善请愿结果。我们在对AI工具推出前后均撰写过请愿书的重复请愿者进行的独立分析中验证了该结果。结果表明，虽然AI写作工具能够深刻重塑在线内容，但其在改善预期结果方面的实际效用可能低于预期，并会引入如内容同质化等非预期后果。