"it's evident that some people are very invested in talking people out of this, which makes me curious"
It's not curious. It's the wish to make sure that people realise that they will not be 'sending a message' if they spoil their vote.
They will be counted, to ensure that the total number of votes tallies. They will be scrutinised to see if there is any way that the marks on the paper could be interpreted as a valid vote for a single candidate (and that can be checked by candidates and their agents if they wish). But there will be no attention paid to how it is spoiled, just whether or not it is. No record is made other than the total, and there is nothing in the results to indicate whether it is a deliberate spoil (for whatever reason) or just confusion, incompetence, leaving blank or whatever).
So if people still want to spoil, even knowing it won't make any difference and their 'message' will be unread and disregarded, then of course that is fine. But people may want to reconsider what they do if they have based their decision to spoil based on incomplete or erroneous information on what happens to ballot papers.
And photography is not banned per se in polling stations, but anything which could erode the secrecy of the vote is potentially a crime. If an election official tells you not to (even if you think then wrong) then you must not do so. Making an image (or any other record) which includes the unique reference number of the ballot paper is specifically banned.