I consider it a great error to read the NT, and especially the words of Christ, as documents of social change.
That society has changed and does change (and I think for the better) as a byproduct of the spiritual change of allying oneself and devoting oneself to the Kingdom of God is an excellent thing. But to retroactively apply our ideas of social progress back on the gospel, as if making good governments were Jesus' main point - or even one of his main points - is a dangerous stretch. You can only get there by making large assumptions, generally unwarranted
For clarity, I am referring to all sets of political ideas that grew up between 1750-1850 that we feel the NT must, just must, be in favor of: socialism, nationalism, communism, free market, self-determination. They are good or bad on their own merits, and have their derivations from NT ideas or not. But they can only be derivations, never the command. The Church had no earthly power at the time of the NT, and the distinction between believers and authorities was clear. As the church moved into the authority business itself, the way back was sundered.