You simply don't understand math if you think that every couple (or even most couples, in practice) having only a single child is sustainable to infinity. You are the only person here who brought up the 3 number; 2 on average is (very obviously) all that's needed to sustain a population, and you chose a higher number (and applied it to the individual instead of as an average) to make the argument look unreasonable.
Also, your assertion that "eventually most do" have at least one kid is already close to statistically false in the US, and if current trends continue, will be false very soon (with the story being the same, or much worse, in all other first-world countries). Go check out /r/ChildFree on Reddit if you want to see just one of the many social movements surrounding this.
You’re correct, it’s not sustainable. But that also means the OP thinks anyone who doesn’t contribute to sustainable model (>=3 children) is an awful person.
Well, 2 is not sustainable on average right now, because we’re below replacement level, so we need to get the average up to like 3, then back down to 2.1 if we want somewhat same amount of people like right now.
Either way, judging people with their ability, want, or need to have children is kinda stupid. I have dear friends who are single, couples with no kids, couples with multiple kids and etc. Actively saying one choice is bad is the reason why some people might actually not want to be around those people. Let people make their own choices, and what they think is right to them.
Again, I’m saying this as a person who is planning to have children.
> that also means the OP thinks anyone who doesn’t contribute to sustainable model (>=3 children) is an awful person.
The OP did not say that, for one thing. You're the only one who's used the "awful people" phrase (which is what makes that a strawman, as I pointed out several comments ago).
OP would prefer to raise his kids to see reproduction as a positive aspect of life, as opposed to the current secular "wellll, you can do whatever you waaaant, but it's a whole lot easier and more fun if you just go ahead and kill your bloodline" that's a logical extension of your pseudo-enlightened "no one choice is better than the others" non-answer (only a logical extension, of course, when ignoring self-preservation and societal preservation as legitimate concerns).
I don't know what country you're in, and I don't know if things are actually different there or if you've just convinced yourself that as long as you don't see a problem with your blinders on, there isn't one. But with regards to "let people make their own choices," someone already threw that argument out (in a different context) elsewhere in the thread, and received lots of good answers explaining how we live in a society and you (and your kids) are affected by everyone else's choices, one way or another: https://news.ycombinator.com/item?id=42705948
Although again, OP didn't even say those people shouldn't exist. He said his family's able to get by without them, and correctly identified that they are not reproducing, expressing optimism that future generations won't have to co-exist with their ideals anyway (I can't say that I share that optimism; there are too many do-as-I-say, not-as-I-do folks around, as well as people like you who may facilitate the spread of bad ideas beyond the bloodlines they kill off out of some sense of respect).