WC, to answer your question. No, I don't think that by saying vigilantism is wrong, people are expressing sympathy. And just by saying it is wrong, nobody is saying they don't understand the impulse behind it.
Fact of the matter: If I witnessed my wife or daughter being raped, I would almost certainly beat the shit out of the rapist.
I would also, on reflection, readily admit that what I did was wrong, and I certainly wouldn't be expressing any sympathy to the guy who did it. I would just, on reflection, wish that I had not performed this act of vigilantism. Why? Because if everyone followed those same impulses, the whole world would be a disaster zone. And also because by performing this act of violence I would possibly end up in prison, which would hardly be helpful.
Adde to that, there are many cases in which a misunderstanding might result in such vigalante acts, which is why a thorough justice system is important.
So, clearly, you can think something is wrong without showing sympathy and without implying that you are always right.
Sorry for the bold but you do have a habit of reading the wrong words, or non existent words.