Earlier quoted context omitted.
Playing the piano and playing music with a 25-key mini keyboard controller are both laudable goals but that doesn't mean they're the same thing.
It doesn’t mean that people don’t mean, playing a 25 key mini keyboard when they want to learn to play the piano, either. It just demonstrates the way in which people gatekeep music.
There's a middle ground between the MPK mini and a steinway. You can get a used Yamaha P-series keyboard with 88 full-size, fully-weighted keys for a few hundred dollars. It won't fit in a backpack but it also won't teach you bad habits _if your goal is to learn to play the acoustic piano_.
If your goal is to learn music theory or produce music or anything other than learn to play piano, the mpk is fine. No gatekeeping here.