Well, seeing as how no ethical framework was provided to work in, and I don't feel like fully typing out my own view/situation right now, I'll just add a small caveat: even if one assumes that having children is ethical (in ways beyond fulfilling your own biological imperative), there is still the problem of opportunity cost. If you think having children is good because it furthers some sort of goal you think is positive (eg. "continuing my culture's heritage"), then there is still the possibility that other actions would do more towards achieving that goal. After all, all the time, effort and money poured into having and raising your own children isn't going toward something else.
So, to keep with the example, what if becoming a great teacher or social worker (and really expending all your assets and time towards it) would do more towards conserving your culture's heritage than just raising your own kids? After all, a teacher could inspire many more children than you could possibly have yourself. Mind, 'perfect' is the enemy of 'good', but still. I suspect there is a chance that some of the reasons people give are more like post-hoc explanations to justify following their instinct.
As long as your reason for having children isn't something like "to specifically raise my own genetic offspring", which is basically just following your biological instincts (which isn't automatically bad), you have to wonder if there aren't better alternatives toward that goal (and even then, adoption could fulfill the need of raising a kid, while donating sperm/egg cells to a fertility bank could help ensure to continue your genetic lineage).