It is enormously useful, and became much more practical as computer technology advanced, especially in the 1980's. (it is necessary to turn thousands of individual radar-returns into a 2-D or 3-D image, a process that became far easier with the advent of high-speed computers in the 1970s.)
We can try to imagine how SAR can be used for "the complete enslavement of the human race", but nevertheless I don't see very much, even when I turn my "paranoid-mode" dial up to "11".
This particular satellite is said to have a resolution of 6 meters. It's hard for me to imagine how being able to detect voxels (3-D pixels) of 6 meter on a side, from space, could enable "the complete enslavement of the human race". It could detect the existence of houses and cars, but those items have been detectable from space since the 1970's using optical satellites.
In the 1990's, space-shuttle-based SAR was used to identify the ancient city of Ubar, found primarily by noticing the lines on the map produced by hundreds of years of wagon-wheel compaction of the deserts, which could be identified and imaged under feet of sand.
It can be used to detect bulging of a few inches height, over an area of tens or hundreds of square miles, such as was done over a place called Sisters, Oregon, starting in 2001. Google 'Sisters Oregon SAR magma bulge' for some details. One result
The underwater analog of SAR is called "side-scan sonar", which was developed in the late 1970's and 1980's by (among others) Harold Edgerton, late professor-emeritus at MIT. This can be used to accurately map seabeds, as was used in the recent successful search for that Argentine submarine that sank about a year ago. (and in the as-yet unsuccessful search for that missing Maylaysia aircraft. https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_370
I don't claim (and it would be foolish to claim) that there are no "anti-freedom" applications for SAR. But I cannot imagine many of those, compared to the others.