Population taboo isn't the problem. The problem is pleading and attempting to dictate to a person what they should and shouldn't do with their personal life. Considering the USA has actually had the fertility rate drop below replacement levels recently, I think it's a bit silly to tell someone to actually have less babies, and at the same time suggest adoption as a (more costly) alternative.

I'd sincerely suggest you reconsider looking into adjusting the quality of life in countries where high birth rate is actually a problem before telling someone how many babies they should or shouldn't have in a country with a fertility rate below replacement levels.