I kept looking for a concluding remark at the end of your article in the hope to know which side are you swinging towards.

Anyway, let me add couple more perspectives to the 2nd child conundrum:

1. If one of the partners has a strong view on the 2nd child and the other is indifferent, go for it. Like you adjusted to the first one and setup your life around them, so would you with the second one. But, at least, you won’t live with regrets.
2. Think future, think 20–25 years hence, when you are 55–60 years old with another 20 years to live, when you would have done it all, seen it all and pretty much be dusted with the busy phase of life, what will keep you going? what will you look forward to? What will be the joys in your life then? Will one of the biggest joys be spending time with your children? In that case, hedge your risks and have a second one. p.s. I see it in my parents case, their life revolves around their children as they have hit their mid-60’s
3. The whole theory around we do the 2nd one for the 1st has some merit in it. I can site numerous examples of folks who share such strong bonds with their siblings that their emotional needs are pretty much fulfilled by the siblings. A 30 minute call every week with the brother/ sister is enough to keep the mind at peace. It gives them a sense of security and belonging in this lonely world which is full of friends and strangers.
4. Continuing on the point above, the world is getting dispersed. Our families are getting dispersed. It is difficult to remain connected with your parents and close friends, let alone first cousins. As a single child, you are depriving him/her of the joys of so many relationships in life — Brother/ Sister/ Brother-in-Law/ Sister-in-Law/ Uncle/ Aunt. Who will the child celebrate the festivals with? Who will the child share his good or bad news with? Who will track the child’s journey in life? Who will organize his wedding and his children’s wedding? Who will the child travel to meet up or plan a family vacation with? Whose children will his children grow up with? And so on and so forth? If the answer to this question is that all of the above will be taken care of through friends, then hope as hell, that your child is a socially capable being whose ability to make friends is excellent
5. Having a child is a difficult decision, it changes your life, it forces you to take more responsibility, it forces you to grow old and mature. But, it is also transient, children grow fast, time flies, lo and behold, they have got a life of their own with a set routine and they have no time for you. Suddenly it appears a lot less work and leaves with a lot more time for yourself. You can go out your friends, you can do things on your own, you can run, jog, blog, trek, hike, dance, jive, write, read, listen to music, hang out and pretty much everything else without them becoming an impediment. So, its basically dedicating a good 7–8 years of your life and then regaining control past that
6. It strengtheners your family bonds. It fosters multiple points of view in the family, in the example above, you mentioned how the parents ganged up against the child, with 2, you could have so many possibilities of ganging up in the family that it only points towards an environment of debate, discussions and encouragement of multiple points of view
7. It grows you as a person, it did for me, somehow, with the first child, i was a half father at max, doing the bare essentials but knowing that there is another responsible adult to take care of the child. However, with the 2nd one, you are not left with a choice, you have to dig in and do your bit. and guess what, it is so thoroughly enjoyable that you regret not being fully there earlier.

So, let me conclude with my 2-bit. If you have decided to have children, go for 2, give them the choice to experience some of the most wonderful relations and bonds that the human species so uniquely has to offer. Give them the choice to draw on the comfort of having someone who shares their parents, upbringing, value system.