I don't know how a self-destruct code will work, but if you have password A get into profile A, while password B gets you into a plausibly looking and normal profile B while profile A and password A get deleted, then you can claim your phone was always and ever the way profile B shows it. It doesn't look or feel "destroyed." It's just a normal profile with mundane messages, browsing history, contact list that makes sense, etc.

Good luck proving that anything fishy happened when the whole operation looks and feels like unlocking a normal phone.

You can even setup biometric login to be password B. So if someone gets into your phone with a fingerprint, which feels very normal, they see a normal boring and completely plausible profile.

There is absolutely a way to make phones secure if there is enough will.

That said, it's a political problem that's begging for a political rather than a tech solution.