This is a really dangerous, reactionary notion. If there's something inherent in our social formations that are translating themselves into our public spaces and we are unhappy with, let's work to change them together. This is a thoughtful piece and I think there are great reasons to delete your posts from long ago because, well, people change! Other commenters here have made good supporting arguments for this.
But we must be very, very careful not to demonize tools where their users need to be taken into consideration: unless there is something specific about facebook, unique among other social networks, that is toxic (this may be the case!) then we need to be wary of these arguments because they are very easy to apply to all social media which, imo, is a copout.