I would expect the "a monad is just a monoid in the category of endofunctors, what's the problem" article to include humorous images. I would expect a serious tutorial about monads to not do so.
You went from "Images should above all never be funny," to "You get this jarring tonal whiplash when you add funny images to an otherwise serious text."
Yeah, if a post's text is 100% serious, then yes it would be jarring to insert funny images. Nobody's suggesting you do that, though.
>It also appears insecure and juvenile, as though you're not fully confident that what you are saying will stand on its own without attempts at comedy, and ironically raises questions about the age and experience of the author.
This comes across to me as strangely judgmental and narrow-minded about what good technical writing is.
Joel Spolsky is, in my opinion, the best software blogger of all time. His posts often integrated humor, and I think it definitely heightened rather than detracted from his writing.
Look at the bloggers who are most popular on HN: Paul Graham, Julia Evans, Simon Willison, Rachel Kroll, Terence Eden. All of them often use a lighthearted style and integrate humor, often with humorous images as well.
It also appears insecure and juvenile, as though you're not fully confident that what you are saying will stand on its own without attempts at comedy, and ironically raises questions about the age and experience of the author.
Of course there are exceptions, but as a rule of thumb, I would strongly avoid this pattern of communication.