alt Hacker NewsiMessage is more conversational because it's what most people are used to using and seeing. People generally associate green bubble messages with spam/transactional messaging and blue bubble with trust. Additionally, iMessage also has additional features such as typing indicators and reactions (likes and loves) that makes the interface feel more conversational. WhatsApp could also be very conversational, but most people in the US use iMessage.
Reading your responses it seems like your angle is to fake looking like a human by using the blue bubble. Are you worried your users will ruin the trust of the blue bubble thus killing your product with your product?