You can't really moralize linguistic drift. By that standard your usage of "dumber" is grammatically incorrect with the 19th century English usage of the word Dumb. Language changes, grow up.
You made a comment elsewhere in the thread saying that HN was full of boomers.
Now it is clear you just actually meant people over thirty, which makes it true. Your usage of "boomer" has not yet passed into the main stream; it is not comparable to "dumb". Google Books easily finds a 1930's reference for the usage of someone "getting dumber and dumber".
I'm not moralizing, by thew way; dumber isn't a moral flaw. (By the mainstream definition of moral; maybe you have your own version of that too).
Hate to break it to you, but it passed into the mainstream years ago.