[paintman252]

That's just not true. I've been in many very online leftist communities and they also freely use it.

it's just general internet speak at this point

[deathanatos]

I view its etymology like this,

              Lil B
    (based ≈ doing your own thing (in a good way)
             not swayed by critics)
             ↙           ↘
       Gen Z             4chan
   (based ≈ cool)        ("based and redpilled"
                          ≈"unswayed by pop rhetoric"
                           and "sees the world beyond the 'illusion'", resp.)

[sangnoir]

You may be ignoring context in this specific instance: the picture in Musk's tweet has "Woke AI" and "Closed AI" being chased off by Based AI.