First, it's not practical. We only have direct control over one person, after all, ourselves. To skip over the one person we have direct control over in order to try to control other people, who we do not have direct control over, is unwise. If we can't master direct control, why do we think we'll be able to master indirect control? This is the meaning of one of Jesus' most famous statements: "Why do you see the speck that is in your brother’s eye, but do not notice the log that is in your own eye?" You can't be expected to be correct about someone else's judgment if your own judgment is skewed. It's also the idea behind the movie To End All Wars. How can I bring about peace on earth if I am not willing to be a peaceful person, the type of person who could actually live in a peaceful world? As the old saying goes, "Let there be peace on earth and let it begin with me."
This may make it seem that focusing on oneself and the inner restrictions to our freedom that the cardinal virtues free us from is entirely a pragmatic affair: we're not doing it because it's the right thing to do, but simply because if we want to gain more and more control over everything, we have to start with ourselves and build outward. In fact, maybe it's even the wrong thing to do. Under this scenario, we are to focus on ourselves before focusing on others.
But that leads me to my second objection. Trying to change the external world rather than ourselves it not just impractical, it's immoral. It's the attempt to manipulate people into doing what we want them to do. As Dallas Willard writes in The Divine Conspiracy, when we engage in such behavior
We are making use of people, trying to bypass their understanding and judgment to trigger their will and possess them for our purposes. Whatever consent they give to us will be uninformed because we have short-circuited their understanding of what is going on. … As God's free creatures, people are to be left to make their decisions without coercion or manipulation. Hence, "let your affirmation be just an affirmation," a yes, and your denial be just a denial, a no. Anything more than this "comes from evil" -- the evil intent to get one's way by verbal manipulation of the thoughts and choices of others.
Kingdom rightness respects the soul need of human beings to make their judgments and decisions solely from what they have concluded is best. It is a vital, a biological need. We do not thrive, nor does our character develop well, when this need is not respected, and this thwarts the purpose of God in our creation.
This was brought home to me recently when I watched a video on the genius of Tyrion Lannister from Game of Thrones. Tyrion succeeds not by trying to force people to do what he wants but by trying to get them to think that they want what he wants.
I have no problem with this idea simply as an observation of people or as indicative of good character writing. But the video recommends this type of behavior to its viewers, and many of the commenters seem to take it to heart. I find it horrifying: what kind of a life would that be? How miserable and empty must a person be to live a life like that? It almost seems worse than death.
Now I'm treating changing internal conditions and changing external conditions as if they were mutually exclusive: obviously we should do both, and everyone does do both. If the speck in your brother's eye is a violent crime he should be stopped from committing, then it is not moral to ignore it until you remove the log in your own eye -- nor would Jesus or any of the other advocates of the cardinal virtues suggest otherwise. The question is the priority. If trying to change others is your fall-back position, if your immediate instinct in all circumstances is to blame other people or external circumstances rather than your own character, then maybe you need to take stock. And, as I mentioned in the earlier post, I'm no better than anyone else in this regard. I have lifelong character traits that blame others instead of myself, and my attempts to improve my character are sporadic and trivial. I have found that it is not true that recognizing the problem is half the battle. It's barely one percent.