To be clear there will be a paper as well. But let's say the gov raids your house and takes your paper with 24 words, that's it....bye-bye. But if they raided your house and took the 12 word seed, you can still have this in your head with a passphrase.
In such a scenario there are way better ways.
For example:
(1) You could encrypt your 12 seed (backup) with a strong password only you know. The gov won't realize what it is, they might recognize that it is encrypted (because it looks like random stuff).
(2) You could use steganography (hiding information inside pictures/videos/audios) to hide your (encrypted) 12 word seed. You might simply choose a granny porn to hide your information inside. I bet the gov won't watch all of your videos and search inside them for hidden information.
(3) You could use an 'offline form' of steganography. You might encrypt your seed, print it out (in hex) and place it somewhere, or print your (encrypted) hex seed onto a cup or something else. The gov probably won't take all of your cups with them to type the hex code into a notepad just to realize it is some random stuff (might realize its encrypted).
IMO these 3 ways are better than completely memorizing a 12 word seed.
And if you do have a paper backup anyway, why do you need to memorize the 12 words?