"Rant" is too strong a term. My guess is that the recent tragedy in Knoxville, Tennessee, your long-standing concerns, and the escalation of hate and fear filled political rhetoric during the election season combined to fuel your composition. In any case, every thing you wrote deserves serious response.
(1) "Why repeat the idea twice in succession?" I might suggest parallelism is at work here, but how could one know for certain? Persecution is the linkage between the two sayings. How can persecution ever be considered "blessed?" I think our two previous posts answer the question, and that we are in essential agreement.
(2) Jesus and righteousness go together in the Christian tradition. In some sense, for us, he is the righteousness of God made manifest in a genuine human life. The one speaking the beatitudes is the embodiment of those beatitudes. To be persecuted for pursuing the kind of righteousness defined by the beatitudes is to be persecuted for the sake of Jesus, at least to a Christian.
To pervert the person or teachings of Jesus in support of hate or fear-driven agendas is the worst kind of heresy (and I do not use the term lightly or easily). From my perspective as a Christian, to do so involves the same kind of evil as is involved in taking the Lord's name in vain. And, yes, this may well be the greatest visible sin of the Christian movement in America at this time.
The challenge for those of us within Christianity who oppose such perversion is how to stand against it without taking up its weapons: slander, double-talk, fear, hatred, violence and the like. After all, we follow Jesus (however poorly), and he refused to allow his disciples to take up arms in his defense or to advance his cause.
(3) I come back to the beatitudes and to your point about a "behaviorally measurable definition of righteousness." I agree with you that we can find it in the texts before us. We're also forced to consider the matter of the inner life, attitudes and motivations and such. Much of the remainder of the Sermon on the Mount fleshes out the attitudes and behaviors called for by the beatitudes.
As you hint, the problem comes at the point of application. Grey areas become evident, humility or even confusion driven doubts emerge--it's much harder to follow Jesus than many a Sunday School suggests!
At its best, community (whether the community of a few trusted friends or a larger one) has something to offer at this point. Community, whatever else it may do, thrusts us into ongoing conversations with one another. Our ideas and attitudes and actions may be challenged, affirmed, broken or refined. Communities, of course, can become clans or mobs. This possiblity does not negate their potential to serve a crucibles of reflective righteousness.
Well...enough. This is a discussion I would love to have face to face, perhaps over Mexican food.