Think about the purpose of reproduction. Nobody cares about it anymore, as evident in declining birthrates and three hundred million aborted Chinese babies (just let than number sink in for a minute, it's more than the deaths from every war fought in the Twentieth Century combined). Reproduction is old hat. In fact, it's so old hat people get offended if you even bring it up. But think of the purpose of biological life for a moment and you'll see it all comes down to reproduction, but what's the point of that? This goes beyond asking why sex exists at all, why did bacteria divide long before sex existed?
It's real simple, but it may come as a surprise. Reproduction is an attempt to cheat death. It's a clever gambit that's been going on for billions of years. At least they tell us it has. There's no real way to tell just how long life's been going on, as I mentioned earlier in "Dreaming of Genesis" and "Dating Anything". It's based on a misperception, that just because something seems old does not mean it really is, but we're talking about appearances here. The truth may be we're in the Matrix and everything is only a hundred years old, or however old the oldest human is. However far back living memory goes there's no way to tell if it ever went back any further, but that's a different topic for a different day.
Let's just say it's billions of years old because that's what convention says. It doesn't really change how you live your life either way. Over time a cell accumulates damage that it cannot repair, mostly from free oxygen, but also from cosmic rays and other environmental hazards. At this point the cell can do one of two things, either it can die or it can divide and give half its damage to each new cell. Now, these new cells can never be as immaculate as the original cell, which started out with zero damage, so over time this whole thing is winding down unless the cells can get smart enough to find a way to repair all the damage. That's the whole point of reproduction: the cells are trying to cheat death long enough to find a way to defeat death for good. Reproduction delays the inevitable.
And somewhere along the line complex forms develop (or don't, but that's another topic), and now they can't well divide in two because there's a brain here and a heart there and to split all the cells in half and restructure everything would be too difficult, so sex has to be invented. Special cells have to be produced that can divide trillions of times and form a whole new body. And you need to bring two members of the same species together for the same reason that bacteria swap genes (plasmids: special bits of DNA that can deliver genes between different bacteria), because otherwise you keep producing copies of the same exact thing and if something comes along and knocks one off then all of the others will be susceptible too. That's why you need diversity.
Now, why there has to be two different specialised units coming together rather than have every individual be a hermaphrodite I can't really say. That part doesn't make sense to me. Maybe it's a trick. Some designer set it up to trick males and females, who aren't all that alike, to come together out of some sadistic joy in seeing if they can get along long enough to reproduce, who knows. These bacteria not only became smart they became psychopathic too, maybe.
Whatever the reason, now you have a system in place where these cells can keep at it, keep multiplying, keep cheating death just a little longer. All in the hope that one day one individual will become smart enough to find a way to repair the damage and then the whole business of reproduction will be over. There will be no reason to make new cells because the old ones are now immortal, or at least until a black hole destroys them. They'll keep making new cells until they figure out how to get rid of the black holes too.
Think about it. You're a door. Through you energy is transmuted to make more people, themselves destined to suffer, reproduce, and die, to keep this race going until either death or the cells get the upper hand. For each individual it doesn't much matter, does it? Unless you're on a farm and you need lots of kids to help plough the fields and milk the cattle, but for city dwellers, for individuals there's no real purpose for any of this, is there? For society yes, for life, yes, but what is the individual supposed to do?
Well, that depends on the individual. Where do you place your faith, in your own abilities or in some promise of a future where descendants you may never see get to live in a paradise on Earth that may never come to pass?