The best that can be done, where possible, is to edit each comment down to whitespace, save that, and then delete it. But yeah, probably still not technically good enough.
I archive (in multiple places, including locally) all of the threads that I add as sources to my personal knowledge base. I'm sorry, but shared knowledge and wisdom I can refer to in the future is more important than your "protest voice" against a centralized platform.
I recommend that if you want to delete something, then delete your account only. Your username won't be visible, but the content still will be.
