Is this legal? Or don't I want to know?
In the USA, at least, the answer is ... annoying.
If you own something it is legal for you to make a personal backup copy. This means it's legal for you to rip your physical media.
*However* it is likely illegal for you to circumvent *any* copyright or anti-piracy mechanisms no matter how strong or weak. For example, most DVD's were protected with an encryption scheme called CSS. CSS was completely defeated which is why it's so simple to use software like DVDShrink or Makemkv or similar. And that software is likely legal because it's not inherently illegal to read an encrypted disc. The digital copyright laws are very strange in this regard and rely on the intent of the encrypting party. This means it's likely *illegal* for you to rip your own discs.
You can backup your physical media.
You can decrypt your own physical media, too.
But it is likely illegal to decrypt physical media which was encrypted by others if they encrypted it with the intention of preventing you from decrypting it or creating copies of it.
It's not illegal to defeat encryption. It's illegal to defeat encryption to enable activity against the desire of the encrypting party.
I could create a zip file and give it the password "12345" (hey that's the same combination on my luggage!). Anybody could readily open this file either by guessing or cracking weak encryption.
It would be legal for me to do it with the file *I* passworded. It would be legal for a third party to do it if I gave them explicit permission to do so. It would be legal if they did so explicitly for the purpose of researching or understanding the encryption scheme.
It would be *illegal* for a third party to do it with the intent of using the file in a way I did not intend.
That said, it's highly unlikely that an individual will ever get in trouble for this because media groups do not want an individual fair-use case to potentially dilute the current assumed power of the law should they want to use it against folks looks Kim Dot Com, for example.