If your goal isn't altruism then why ask "Why isn't it more ethical to produce as many children as will fit in a female's lifespan?". Simply get as many children as you want to have.
The "and" in my reply connects two separate conditions. It is possible that your goal is altruism but you don't value people equally. The question of whether having many children is ethical could depend on exactly what factors you use to weigh your children over strangers.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.