It's clear that Flyertalk is mostly savvy travelers who know the rules and expect everyone else to as well. However, many people have no idea what basic economy is, and the airlines and OTAs don't always do a good job of explaining it.
At the end of the day, the airline is going to have to find a way to let the kids sit with at least one parent, because it's too risky not to. I know there is currently no law requiring it, but there was no law against removing Dr. Dao either, and look how well that worked out for Untied. Publicity can be stronger than any law. What if a child gets molested by another passenger while the parents are in another row? What if "my autistic son had a panic attack because Mr. Diamond-Guest refused to let me sit with him" goes viral on social media?
Right now, congress has asked the government to look into the matter. This is basically telling the airlines "this issue is on our radar, fix it before we make you". If they don't, the government could force airlines to keep families together under threat of fines per incident.
To all of you who are saying "it's her fault and she can deal with the consequences", reality doesn't work that way. Most people don't care about the details about fare class and seat selection, but will not stand for kids being separated from their parents. If airlines don't sort this out, DOT will do it for them.
I feel for the man who had to move to a middle seat, and I would have hated to be in his position, but seat assignments are not guaranteed and can be changed by the airline at any time, per the CoC. It's no different from being made to move to another seat due to a FAM, equipment swap, service animal, or any number of other reasons.