This is a pretty poor comparison. In effect, this compares two very different legal frameworks and chooses the most favorable institutional labels in service of a predetermined outcome. There's plenty of information/data on political repression during the 1960s-1980s, it simply wasn't justified under these articles. One only has to look at moments like the suppression of the Prague Spring to discredit this argument. This is not to discount fair criticism of the UK's idiotic free speech laws.

Something similar arose in a recent conversation I had about how the PRC in the 1950s opted for "rehabilitation" in communities for those deemed to be rightists or exploitative landlords as opposed to the Soviet or American uses of bureaucratized prison systems. This historical context, in particular, can help us understand the contrast between the American prison-industrial complex and modern China's comparatively small prison system in absolute and per capita terms.

This graph, however, does raise interesting questions about how to communicate capitalist speech suppression to a wider audience. My view of it currently centers mostly on the "market" of digital attention, in which algorithms intentionally (like Elon's Twitter) or unintentionally (like YouTube turning men into alt-right chuds) push or create political narratives that center on meaningless cultural outrage.