The question by the OP wasn't "is political violence ok?" Though.
So the results on the poll are probably skewed by the linking of this murder to meaning people as a whole/a particular group of people don't believe in free speech, or if people don't feel sympathy for him or in some cases actually celebrate his death, then they don't believe in free speech and then the division along left/right fighting.
The poll isn't really a clear question so taking meaning from it is of limited value at best.
If the question is simply is "freedom of speech isn't tolerated by some?" A true statement then the answer should be 100% yanbu because it's unequivocally true. The Taliban, Donald Trump, those who criticize JK Rowling are all anti free speech for example.
But the poll can be taken a lot of different ways in which a yabu means "nah killing Kirk and political violence is fine"
I voted yabu because I think it's disingenuous to link the two based on a violent criminals violent crime unless you're going to talk about the persistent erosion and attempts to censor from both sides.
Kirk supported a man who tried to overthrow a Democratic election and disregard the expression of millions of Americans, so you can lump him in with the people who don't believe in free speech if you want to take a broad interpretation.