The post I was replying to was not worded as "the last era of X". It was worded as "the last era of humanity". Certainly things, practices, places, peoples, beliefs come and go. Humanity likely will end at some point, but that's not about to happen in any predictable way in the currently foreseeable future.
Incorrect. It was worded as "the last era of humanity doing X". It parses as "the last era of {humanity doing X}" and not "{the last era of humanity} doing X" (which isn't something that makes sense anyway).
