Computer-mediated communication (CMC) tools are used to increase social interaction in collocated settings. Recent research has been primarily constructive (oriented to building of systems) or phenomenon-driven (serving attempts to understand interactions in collocated CMC). The paper contributes a theory-driven approach and examines collocated CMC as a Habermasean "public sphere": a space that supports inclusive, civil, and rational discussion. An in-the-wild experimental study comparing CMC with face-to-face (F2F) communication enabled ascertaining that CMC is more inclusive than F2F communication. Respectfulness levels did not differ but were established differently: via collective construction of a common narrative in F2F and through quick reactions in CMC. Similarly, while rationality figures were on a par, F2F communication allowed participants to justify their claims better. The article discusses how a theory-based approach can strengthen phenomenon-driven research with new conceptual frames and measurement tools, and steer constructive research with a normative framework.