I think in the case of the original tweet it is gatekeep-y - in making fun of someone for being "only" an HTML/CSS coder, or telling them that they aren't a programmer, they might be driven out and not continue on to learn a "real" programming language.
This happens more to women than men so maybe we just see it more and are more aware that it happens.
Yes, the tweet did have that tone to it. No doubt people use the "HTML is not a programming language" stance to belittle others. Which is ridiculous and unacceptable. I just don't think it needs to be called "programming language" to be considered useful and a worthy skill.
"Programming" is really a specific area of Software Development.
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