Data: Compared to the 1970s, support for free speech is lower among college-age Americans

Since 1972, General Social Survey participants have been asked the following question: "Consider a person who believes that Blacks are genetically inferior. If such a person wanted to make a speech in your community claiming that Blacks are inferior, should he be allowed to speak, or not?"

I wanted to look at trends among college-age students. Here is a graph (sample size = 2,158):

The green bars indicate the percent who would allow the controversial person to speak. This has fallen from 68.4% during the 1970s to only 48.0% in this decade, a drop of 20 percentage points. 

It looks to me like young people in the 70s were either more open to genetic ideas concerning race, or they were simply more supportive of free speech. 

Another interpretation is that young adults in the 70s were against the establishment and thus favored ideas that challenge the mainstream, while young people today tend to support the establishment and thus support its suppression of unpopular ideas.