As far as we know, for the obvious reasons.

You have to remember the cultural context. JFK was a liberal but he was also a staunch anti-communist. The election of JFK brought a new vitality to the US but it also met with staunch opposition and outright hatred, especially in places like Dallas. Remember that Nov 1963 was a year before the next election, JFK was trying to win over texas if it was possible. When he was shot the immediate reaction was an intense sense of tragedy and loss, nearly universally across the country, almost regardless of politics. But also there was the strong immediate suspicion that the assassination was an outgrowth of the intense local hatred for JFK and his policies that had become a significant and notable phenomenon.

Even regardless of Oswald's motives in killing the president there was an intense shame that settled on Dallas for what had happened there given the local sentiment at the time.

Ruby had extensive connections with the local police and was somewhat of a gangster so for him killing Oswald probably felt like less of a big deal than it might for others, and he was certainly one of the few civilians with such an opportunity. But at the time there was an incalculably long list of individuals with a strong desire to visit revenge on the president's assassin. He merely was in a position to carry out such a thing.

JFK's approval rating peaked at about 70%, which you might consider to be the percentage of the population who would be significantly grief-struck when he was killed.