At what point should monuments be guarded for historic reasons.
Imo, speaking from bias for outcome, tear down all confederate statues, save all ancient monuments.
Some of those monuments in the middle east may be of tyrants, but I defend them none-the-less. But if some of those confederate monuments manage to stay up for another 500 years, then my very same arguments for preserving antiquity start to apply.
Only conclusion I really have is to strike while the iron is hot. But what time frame that is is subjective, further this conclusion is somewhat anti-stoic saying it's better to act now then wait and then not be able to tear down a symbol because you've made it into an artifact.