You gotta be able to remember your password, otherwise if you have to write it down and you get physically robbed, you're going to be SOL as bitcoin transactions are not reversable after the 1st confirmation.
The same is true of seed phrases, and yet we all write those down. Just ensure it is stored somewhere securely.
Memorizing 12 English words in a particular sequence should not be that difficult by comparison. Regular passwords on the other hand, the truly random ones with numbers and symbols, cannot be memorized at all. Especially once we get to 20+ characters.
They definitely can by coming up with some memory system, but that doesn't mean anybody should. You shouldn't rely on your memory for anything really sensitive, be that seed phrases or long and complex passwords/passphrases.
Yes if you know how to use these features, nothing bad will happen. It's like the about:config in Firefox or the Windows Registry. But imagine telling a new bitcoiners about BIP39 passphrase. When you combine that with the fact that not all wallets support it (and those that do place it in very different GUIs and screens), it's easy to see how someone can accidentally mess up.
That's a fair point, but making a blanket statement of "do not use passphrases" is not helpful, I think. Rather you should avoid them initially but spend some time learning about how they work to make you confident to use them one day.