Why was the crisis at Kent State so important? What important lessons did the students at Kent State and around the country learn?

There's been plenty of coverage of the Kent State incident. Student protests were trying to bring attention to the horror of the Vietnam War, but they weren't getting a lot of sympathy (much like the BLM protests today). Kent State, where innocent students were killed by the National Guard was so shocking that it made people pay attention- and ultimately contributed to the US pulling out of Vietnam. It also led so some stricter rules for calling out the National Guard, and restrictions on what they could do. As for the "are we truly free" question-- no one is truly free, if that means doing whatever they want regardless of the results. If you want to live in a civilized society, with roads, schools, shopping, movie theaters, bars, restaurants, etc., then you have to give up some of your "rights" to make things run as smoothly as possible for everyone. You're not free to drive as fast as you want, because that endangers other drivers.  You're not free to yell "fire" in a crowded theater, because that's when people get trampled. And you're not free to say "come and take over the government" because that takes away the rights of voters, and results in the kind of mayhem we saw last week. 

Never Trust the National Guard  even if you are Unarmed