You're sort of circling around Kant's Categorical Imperative, which is articulated as, act only in such a way that one would be willing to see enacted as a universal moral law.
https://en.m.wikipedia.org/wiki/Categorical_imperative
When you let that percolate for a bit, you get to, "Treat others only in such a way as you yourself are alright with being treated.
Your self-defense example resonates with this way of life, as the person seeking to do you harm has telegraphed they are fine with you reacting in kind.
You cannot just murder anyone, as if no one is engaging in you, the idea is that one best should reciprocate only in kind. Most moral systems pre Kantian Categorical Imperative, are crippled by not being able to justify being moral as an end in and of itself just from the tenets within the system itself.
I would not, under the categorical imperative, censure either group in this case, as I am not willing to accept mob justice as something I am comfortable being applicable to me. Both parties, however, have have demonstrated that they are willing to accept being treated in that manner through their actions, though Transwomen moreso at this point than the users of KF. KF has merely existed.
Therefore, at this point, any follower of the Categorical Imperative can engage in mob/vigilante justice against either Transwomen/KF with clear conscience, as it has veen clearly evinced, that is how they wish to be dealt with, and this doesn't taint not engaging in mob justice/vigilantism against anyone else, as it is always the first mover that sets the level on which the interaction takes place.
It's where the Golden Rule "Treat others as you would have them do unto you" stems from.
