I don't necessarily disagree with you that there will be people that want more than 21m coins.
An argument like that will never be presented "we want more coins and high inflation for the lolz".
It will be presented as "we want cheap txs".... Arguments like
"People want cheap txs, who are you to stop that".... Populist bullshit like "bigger blocks" and the "dangers" of "fullblockalypse".
There is no comparison between a hard fork to raise the blocksize and a hard fork to increase the 21 milion cap on supply. The former is a minor property that almost everyone agrees will need to be changed at some point. I owned Bitcoins for years before I even know there was a max blocksize. I knew of the 21 MM limit before I bought my first coin.
A slippery slope argument is a logical fallacy.
https://en.wikipedia.org/wiki/Slippery_slopeDude increasing the 21 M limit and increasing the block size is the same thing.