Unless, of course, some people just decide to declare it "not legitimate"...
The agreement in the morning was "We'll race, if you can guarantee there won't be another incident. One more incident, and we're out!"
Well if that was what was agreed, then it was an entirely meaningless agreement. How could race organisers guarantee that one individual living along the route would not act selfishly, recklessly, and with apparently total ignorance of what was going on around him?
If teams are not willing to take part in races that can be adversely affected by the acts of those with nothing to do with the race (protests, vandalism, determination to drive where they want without following instruction, or blatant stupidity) then racing is finished as a concept.
Extending the same "other people must be able to guarantee the safety of everything I do" approach to wider life, means that we had better not get out of bed in the morning.
It is the nature of probability that rare events can occasionally happen in close proximity: it bears investigation when they do, but genuine co-incidence is a thing. I see nothing that might have been done to prevent a recurrence of Thursday's event that could have prevented Friday's (short of confiscating the car keys of everyone in the area).
And I would think it incumbent on those defending the teams that pulled out of the race to explain what they think the organisers could have done to prevent what happened.