I have a life as well and my plans are just as important as the family person.
Indeed, and your post raises some fantastic points, but when/why would your life be so greatly impacted by a seat change? It might not even be the family's fault.
I don't think
Hvr is really making the crux of his point about seat changes (he's just used it as an example). He is just talking about generalised biases toward one group or another that, while sometimes logical, don't always make sense. As he said, if you've got yourself organised, why should you be negatively affected by someone else who hasn't, because of some presumed preference.
For instance, I'm sure everyone groans (either inwardly or outwardly) if the person/s in front of them in the check-in queue have exceeded a bag weight limit and then proceed to hold up the queue by re-packing right there at the check-in desk rather than moving away to an area more appropriate to re-pack and then re-join the queue once done.
Families that leave seeking seats together until they practically board, when ample opportunity was available to do this earlier, is much the same sort of event. Poor planning, disrupting others who did the right thing, without reasonable excuse.
Having children certainly means a lot of responsibility for any couple, and most families are responsible sensible groups, but a few people tend to have forgotten that having a family requires a lot of hard work and tend to treat it a little too lightly. Not everyone is perfect, but if you expect the world at large to bend over backwards to suit you, when you've done little to do anything yourself - it's no surprise it will put some peoples noses out of joint.
So I don't think Hvr is anti-families, just anti those who use favourable biases as their go-to plan without trying to be a little pro-active beforehand. I think that's an understandable point of view.