I don't know why he's doing this, but I can't say I care either. I just care about the fact that perfectly good information that could be of benefit to site visitors and users is being tampered with so as to be of no use to anyone.
Surely destroying information, especially information that is community approved and accepted as answers, is not what Stack Exchange is all about.
I could rollback the source, but that seems a mere bandaid and does not remedy the behaviour that motivated it.
What is the community's preferred approach to dealing with this? Does this merit moderator action?