What considerations should be made when voting?
The premise of the question is flawed in that it proposes there could be some consensus about how people vote. Voting is not by consensus, it is everyone's expression of their own opinion.
I know you already replied to that
When your opinion becomes a crusade affecting hundreds of questions and answers, then it's a bit more than an opinion.
No, it is still just an opinion of one user, who happens to think that those Q&As should be deleted. Perhaps I hold this opinion a bit stronger than others hold theirs, but I am not responsible for other people's weaknesses. I see such Q&As as broken windows, through which new users enter (via Google search, typically), and conclude that the site is of low standards. I don't want their first sight of the house to be an overturned trash container.
If others' opinions lean toward inclusionism over deletionism, they can express that by their votes, too: upvote, reopen, undelete. The fittest will survive.
###Mathematically good answers
Mathematically good answers
I don't see mathematical correctness as a sufficient condition for preservation. Wolfram Alpha generates mathematically correct answers (with more details in the Pro version), but it would not be useful to have its input/output pairs to be logged on this site as Q&A pairs. Which isn't much different from what is going on.
Asker: How solve $\int \frac{\sin(2/x)}{x^2}\,dx$? HALP! (Question titled "Calculus problem help")
Answerer: Hint: Try the substitution $u=\color{blue}{\dfrac{2}{x}}$, so that $du=\color{blue}{-\dfrac{ 2}{x^2}dx}$ (Makes no edits to the question)
Others: Gosh, that's a mathematically good answer, and now the whole thing is sacrosanct content destined to stay forever on the site!
View from the sidelines
It's sometimes interesting to find how the site is seen by someone who does not participate in it, but pays attention to what goes on around the network.
I recommend this post by MichaelT to your attention.