Part of the reason I’ve been (perhaps too) subtly alluding to the fact that Jesus was forming a new nation with his commands is that this also militates against reading a public-representative exemption into Jesus’ commands.
Consider: the lex talionis was a command given to the nation. The nation of Israel, through its representatives, was commanded to take the life of murderers (for example).
But consider just the context of the Sermon on the Mount: Jesus is firstly standing on a mount, giving a discourse about the law. This immediately alludes back to Moses giving the law to the nation of Israel. Thus we have one indication that Jesus is forming a new nation with a new law in this passage.
Secondly, Jesus says those listening to him that they are “the light of the world”; but it the OT this was the calling of the nation Israel. Thus we have a second indication that Jesus is not speaking to just a sector of society (“private citizens”), but to a nation as a whole.
Thirdly, Jesus calls 12 disciples, signalling that he is remaking Israel. This is another indication that Jesus’ message is about re-creating a nation, not just a sector of a nation.
Further, outside of even Matthew, there is the consistent NT teaching that the church is a nation-state unto itself: look at the Petrine epistles and Revelation, just as obvious examples.
If this general point is correct, however, we have an interesting implication about pacifism: it was the nation of Israel, through its public representatives, which was to carry out the lex talionis. But it is to the nation of Israel that Jesus’ prohibition of the lex talionis is directed. In ages past the public representatives of Israel were to kill murderers, now they are not to resist them.
This means that within the new Israel there can be no killing. But there’s another possible way of getting around this point: Christians could be the representatives of another nation, e.g., America or Canada, and thus kill for them, but not for the church.
But this misses a major point: God has restored Israel (plus the Gentiles now enfolded into her) to be a light to the nations. It is precisely in living not according to the lex talionis, but the law of non-resistence and love of enemy, that the church is an example to the state of how it ought to act. Rulers of the world ought to become like rulers of the church; excommunication ought to replace capital punishment. For the opposite to happen is not an example of a Christian being faithful to their calling, but rather a failure to do so.