As the other commentors have said, this isn’t a problem with email services, it’s a problem with email users. If you put all the addresses in the “To:” or “CC:” boxes, its because you want someone to Reply All. If you want to prevent that, put all the recipients in the BCC box.
Its a good idea, but fortunately someone already solved it a good while back. Now we just need a PSA to teach people to stop cramming everyone in the wrong box.
If this is a genuine question, and not a halfhearted attempt at trolling, you need to be more specific about what you’re asking:
Are you looking for biological / evolutionary theories about why maaaaany animals show same sex sexual activity?
Are you looking for an anthropology/historical analysis of how human sexuality has been expressed in different ways and had very different norms and taboos than our current blend?
Or are you asking individuals to talk about their own experience and what lead them to identify as whatever?