In the actual 1960s ... the Free Speech Movement of 1964-1965 that you point to was a response to the fact that denial of free speech was the status quo.
> I thought this fight had already been won.
Sure, there was ground gained, at least temporarily, by the Free Speech Movement, but victory wasn't durable. Otherwise, we wouldn't have seen the violent suppression of non-violent on-campus free speech in 1970. [1]
> Free speech seems to be one of those things that institutions and governments need to be repeatedly compelled to respect.
Yeah, there's a reason that it is said that "The price of freedom is eternal vigilance".
None of us is immune to the tendency. Each of us must eternally watch ourselves too. Political maturity comes when we can check our decisions by seeing both sides of an issue and carefully weighing the costs.
[0]: http://www.thisdayinquotes.com/2011/01/eternal-vigilance-is-...