What might the world population be?

Less than the Solar System population.

That depends on too many factors to make any kind of educated guess.

Why?

Because life, and being alive, are good.

Hmm, that seems extremely reductionistic, and sounds like you do not know anyone with bad or unpleasant lives. It also sounds like you're probably pretty young.

Life is by definition good. No other definition of good has any coherence.

The fact that in the vast majority of cases, people who are faced with life-threatening adversity, struggle in an effort to overcome it rather than consigning themselves to death, suggests this is the overwhelming perception held by people.

Natural selection ensures that the perception that life is good will always be the dominant one amongst any species.

You're defining life as a moral good. That is not part of its definition.

I think it implicitly is.