This.
They can eye roll all they like, but they will see the messages and each party has to have a representative agree that the ballot is spoiled.
If you don't up a X but put something that states a clear preference for one particular candidate they can still potentially count that vote.
So if you wrote - DICKHEAD, DICKHEAD, DICKHEAD, I LIKE THIS CANDIDATE, DICKHEAD respectively by each candidate, the candidate you said was alright could potentially argue you stated a clear preference for them and that the vote should be counted for them. The other candidates would have the right to argue differently. They'd have a discussion and a decision would be made with the local officials. If you end up in a constituency which comes down to just a few votes, these votes can potentially become important.
The point is, that every vote has to be considered fairly. Everyone putting Xs makes it easier and so they aren't there until next week but you don't HAVE to do this. There are some legalities which are a bit technical in terms of what else is acceptable.
Its pretty normal for there to be ballot papers saying all kinds of things. Most are ignorable as fringe, but I do have to say that if you were getting quite a number saying similar, even if you eye roll you'd be silly to ignore it completely. Its unusual to see multiple ballots making a similar point on spoilt ballots tbh and it does feel like there is a concerted effort this time around. Remember journalists will be are a lot of these counts - particularly ones with notable candidates, if they see a pattern they see a story.
If your alternative is to not vote, why not? What are you losing by spoiling? If you think the risk of it being ignored is outweighed by even a slim chance of some taking note, then you may feel its the right way to make your democratic right to vote count. I don't necessarily think this goes against the priniciples of the women who fought for the right to vote at all.
Exercising your democratic rights and your rights involving voting don't have to come in the conventional X in the box imho.