What this says to me is that you think survival is the principle of most importance, rather than happiness. But I disagree. There is no intrinsic value to survival, unless it yields a life that supports a happy sentient being. Indeed, people do choose to end their life sometimes, if they see no hope of happiness in the future. Survival is worthless without some reasonable chance / probability / expectation of happiness.
You say it's better to "just not" identify a universal principle, but I disagree with that too. It only becomes a problem if you don't allow yourself to change your mind if you realize that the principle you identified isn't serving you. But this is really no different than what we've already attempted with the Constitution. We made some rules that we thought would serve us, and we have an amendment process to change it when necessary.
Our approach to science is similar. We identify rules and theories that describe our world as accurately as we can, and then we change them when we find better ones. When it comes to happiness though, I just happen to think that we won't need to change it. But that doesn't mean we wouldn't or shouldn’t change it if we realize that it's not serving us. To me though, it seems like it's basically a tautology that happiness is all we want (do you understand why I think that?), so it's hard to see why this would ever change.
My definition of tolerance versus intolerance certainly wasn't intended to mislead or confuse. I do see that my usage is different than how you've described Popper's. But as I think about it more, I feel like my definition is not so different than the common one, and actually serves as a pretty good "least common denominator" of all the ways those terms are used. The main difference, I think, is just that most people use those terms as a sort of "bluster", to signal to an audience whose side they are on, but where there is no expectation that they will have to put their words into practice, and determine the exact boundaries of what they meant. Whereas I'm writing within a context where I'm trying to root out ambiguity as much as possible, and am therefore forced to coerce my words into having a clear definition, even if most people settle for fuzzy definitions of those words in most contexts.
I think the "leniency versus cruelty" question will have similar pitfalls as that of "tolerance versus intolerance", in that the definitions aren't clear. But however we define the terms, the real underlying question is always this: How do we create an environment such that the game-theoretical dynamics will maximize the probability of happiness for as many people as possible? And I suspect that saying "leniency is fine always" or "cruelty isn't fine ever" are both incorrect statements when trying to solve that problem. They are not good as absolutes, even if they are good rules of thumb. And the only way to measure when it is correct to apply lenience or correct to apply cruelty, is by its probability of relieving pain and sadness, and yielding pleasure and happiness in the given context.
Any practical law that we write will undoubtedly fall into this same pattern, in that it will represent merely a rule of thumb, rather than an absolute rule. And we will have to muddle our way through that, as you've said - and as we do currently via the court and legislative systems. But I think it's also important as a society that we establish the true goal of all of these "laws of thumb", which is that they are all intended to produce happiness. And if any rule, in any context, isn't passing that one criterion of facilitating happiness, then we will know that it needs to be changed.
