Kanoim pogim bo is a special halacha regarding bo’el aramis in public, stealing kli shareis, and cursing…. Hashem in the name of avodah zara (mishnah Sanhedrin 9:6) It doesn’t apply to other aveiros, including mishkav zachor, much less the support thereof.
Any other aveirah, even worse aveiros than bo’el aramis(which if done without living together is only derabonon, as it happens to be) require due process and one is not allowed to kill the violators of them.
Toeva parades need a strong, vocal opposition, but what schlisel did was murder. He was a murderer who, if taken to beis din, would have been put to death.
It would be murder if he killed a child molester, murderer (after he killed, since before it would be a rodef case), mechalel shabbos, or anything else. If you see someone do a capital offense and kill him, it’s you who is the murderer. We have laws. We are obliged to keep those laws, even when we want to protest chilul Hashem.
As to whether kanoim pogin bo applies today, see rema CM 425:4, which says that you need to warn the sinner first. Here, no warning was given.
Kanoim pogim bo also has a lot of limitations. It has to be during the aveirah itself. It also needs to be done in front of 10 jews
Also, if the sinner kills the kanoi in self defense, the sinner is not considered a murderer, because the kanoi has a din of a rodef(Sanhedrin 82a)
Yerushalmi Sanhedrin 9:7 is also critical of kanoim pogim bo in general and says that chachamim wanted to put pinchos in nidui if not for the fact that Hashem was maskim to him.