Much of the content of which we speak is months, if not years, old. It served a purpose and was part of a conversation (or debate) at the time, yes; but I doubt there are many people who read through threads that are not current or are more than a month or two old. I know some do, but I'd guess it's a tiny minority. People continually post about topics that have been covered in massive detail in the past, multiple times; but even before the board changes, most people didn't bother to search past threads but just asked their questions, which others patiently answered yet again. When conversations are currently ongoing I get tons of PMs, but once they've sat around a couple of months, getting a PM referring to one of them is a rare, rare event -- the older threads are not being constantly dredged up for their usefulness.
Please remember, the one or two people I know who would like posts deleted are responding to the way that posts can be batted around the internet much more easily and readily than before, in ways we cannot predict and did not previously understand. Those of us with SN kids shared specific information that was important for laying out problems or for proposing solutions or discussing how education works in our homes, information that the vast majority of people on the forum don't have to worry about having disclosed in an effort to get help or to help others.