Imo they intentionally have made the scary misleading warning on f-droid, but at least they don't actively try to stop me from installing it, like the Apple guys do.
Discussion
It's a little more than an F-Droid warning. I am, probably unnessessarily to be fair, afraid AOSP might disappear one day - or be crippled so much that upkeeping things like Lineage or Calyx or alike is made intentionally hard to impossible.
Which would effectively lead to "killing" (i honestly am too braindead for a better synonym right now) those ROMs. Which would be bad...