There might be a bigger post in the works. I'm not sure. In the meantime, consider these:
1. Suicide is currently the sixth leading cause of death in the United States. Why not Somalia or Afghanistan? Because the people there are too busy dealing with how horrible their lives are to even contemplate suicide. They haven't even had the opportunity; that's how bad things are for them.
2. People who claim to be happy in public are often lying, because being depressed is a social taboo that can lead to being ostracized -- especially if one has a spouse and/or children.
3. Many people who legitimately think that they love their lives are only ever asked after things have settled down. Humans are fickle; it's very easy to say that something horrible is "worth it" when it's no longer happening. Ask someone if they're happy right after they've gone through a coincidental string of three funerals in a row and then gotten fired from their job and see what they say.
4. Some people love to eat unhealthy foods, but the subjective satisfaction of eating those foods does not make the foods healthy. Likewise, someone may legitimately enjoy living, but that in no way implies that their life is healthy -- for themselves or for the rest of the biosphere.
Update: Alright, I'm seeing conflicting reports on the suicide thing. Some say that it's the eleventh leading cause of death, which, while still high up on the list, doesn't quite make it seem like a crisis or confirmation of there being a substantial number of profoundly unhappy people in the world. It's definitely still a problem that needs to be addressed by society (not in the "take some medication and pretend everything's okay" way, of course), but the huge variation in data just goes to show how sloppy a lot of modern research is. For this reason, and because of my general skepticism regarding statistics, I'll refrain from citing any sources and just state that suicide happens, which is a perfect reason to not have children.