Despite growing awareness of ethical challenges in software development, practitioners still lack structured tools that help them critically engage with the lived experiences of marginalized users. This paper presents PerspectiveCoach, a large language model (LLM)-powered conversational tool designed to guide developers through structured perspective-taking exercises and deepen critical reflection on how software design decisions affect marginalized communities. Through a controlled study with 18 front-end developers (balanced by sex), who interacted with the tool using a real case of online gender-based harassment, we examine how PerspectiveCoach supports ethical reasoning and engagement with user perspectives. Qualitative analysis revealed increased self-awareness, broadened perspectives, and more nuanced ethical articulation, while a complementary human-human study contextualized these findings. Text similarity analyses demonstrated that participants in the human-PerspectiveCoach study improved the fidelity of their restatements over multiple attempts, capturing both surface-level and semantic aspects of user concerns. However, human-PerspectiveCoach's restatements had a lower baseline than the human-human conversations, highlighting contextual differences in impersonal and interpersonal perspective-taking. Across the study, participants rated the tool highly for usability and relevance. This work contributes an exploratory design for LLM-powered end-user perspective-taking that supports critical, ethical self-reflection and offers empirical insights (i.e., enhancing adaptivity, centering plurality) into how such tools can help practitioners build more inclusive and socially responsive technologies.