I would re-word this slightly and say the only CONCERN we should have is control of self ultimately, as of course, any control we have over others is temporary and not really sustainable in the long term.
As far as budo is concerned, absolutely, primarily I think it is about learning self mastery, which is learning that we need to first be concerned about self than about others.
While this may seem a small thing, I think it is great actually. We need to understand in budo that we do, and can have power over others and at times we need to exercise this power, hopefully in a skillful way....otherwise we run the risk of turning what we do into a very narcissistic practice, which frankly I think happens a lot in Aikido.
through training, you may be able to gain control over others. But you are not entitled to that power by virtue that they attacked you, nor by virtue that you have studied Budo. Therefore abuse of that power is reprehensible. That is why self mastery is key in my opinion. When it isn't put as the singular objective in training focus is lost, and people start to believe they actually have entitlement to and over other's lives. Whether they interpret that sense of self-entitlement as the right to kill another, or whether the interpret that sense of self-entitlement as them having the "right" to choose not to kill some one. IMO I don't believe either should be a choice. We are not entitled to an opinion or any rights over lives we had no part in creating. Whether that means ending a life or choosing to arrogantly flaunt a tainted sense of mercy, we have no right to these decisions over others. And I don't believe we are entitled to stewardship over ourselves when lacking self mastery. If you can't even be your own master, then why suppose you can steward yourself with any sense of justice? Self mastery takes a life time. Which goes hand and hand with my opinion; that you don't have any entitled rights over any life you had no hand in creating...including your own.