And that's perfectly cool. Given a choice between those two options, prison beats crematorium any day. In my opinion. You can make your own choices.
But almost every time I hear it, it's a platitude. It is not said to clarify a truth. No one ever slaps their head and says, "Shit, I was wrong all along. I always thought dying was better! Thank you Mr. Wise One."
The first time I watched a self-defense class was in 1981. I saw a big, burly guy teaching women that if someone grabbed them in a front hug they could beat on the chest of the bigger, stronger man until he would magically loosen his grip and then they could hammer fist him in the nose and they would be safe. Then I saw the instructor teach that if someone grabbed a woman's wrist she should just chop his throat.
Even as a seventeen-year-old with just a couple of months in judo and some weird hybrid striking art, I knew something was wrong: Low levels of force (that wouldn't work) when high levels were needed? And potentially deadly force to a stimulus that might just be a child reaching for your hand? Ineffective AND inappropriate offended me on two levels.
When someone says "I'd rather be tried by twelve than carried by six" and they are sincere, it's simply unnecessary. But in almost every instance that I hear it, it is an excuse. The instructor has some idea of how to hurt a person and absolutely no idea of force law. So they say this to convince the people listening that force law is not nearly as important as what they can teach.
In logic or debate, this would be called a 'false sort.' It only has any validity if those are the only two options and they are mutually exclusive. "I'd rather hit myself in the head with a hammer than stab myself in the leg with a screwdriver." Simple fact is, you can do both of those things or neither. Dying might take going to prison off the table, but going to prison certainly doesn't take dying off the table.
The essence of self-defense law isn't that complicated. If your life is on the line, it doesn't hamper you at all. If you want to Monkey Dance or teach somebody a lesson, that's a different story... but you already know those aren't self-defense. Plus, most of self-defense law makes sense. It's not some esoteric weirdness.
If someone refuses to teach it, it is because they don't know it. If they offer the excuse that they are afraid worrying about the law will freeze you I would question, well everything. Their knowledge, first. Their common sense. Their commitment to your survival over their ego...
There are lots of reasons people freeze. In my experience, scary ignorance is far more freezing than informed fear. "I'm going to get sued but I know the ropes" is far less freezing than, "OMG, am I going to get sued? What will that be like? What should I do?"
One of the keys, though, and even good, knowledgeable instructors might miss this, is that knowing force law isn't enough. The students have to practice articulating decisions. Even most cops could use more practice at that.