I suppose it's a slightly more accurate term. The messages here are not truly private since they are not encrypted, but since they are sent directly no one should read them in the normal course of using the platform. Calling them private might imply to people that other people cannot read them, rather than the reality that it is just very unlikely anyone will. I would also argue that if something is released to an authority it is not "private" even if it is not publicly available.
Honestly, it doesn't really matter which you use. People will generally understand either way, so you can go ahead and keep saying PM and others will say DM and we can all just understand that they mean the same thing.
Very true, it is not required to have a solution, I myself only gave a couple of broad frameworks as alternatives, alongside a call for abolition.
But consider for a moment the people you're accusing of "vigilantism" here. These are people who very often did go through the so-called justice system, for example Aubuchon reported her case, completed a rape kit, then waited a year for nothing to happen. It was only after being utterly failed by the system that she posted on social media, with the intent of warning others about this creep. He does not deny having sex with her, on the job while he is in a position of power over her no less, but says it was consensual. Remember, she was only 18 at the time, and has no wealth to speak of. What else was she supposed to do in this situation?
Or take Longhorn's case, she followed all the appropriate channels, and got nothing but grief for it. An official complaint to her work led to harrassment, and her case was dropped by the prosecutor because he thinks she should have fought him off. Here we have a member of the justice system itself advocating what could reasonably be interpreted as "vigilantism" in favor of the official legal channels. According to Wikipedia: "Vigilantism refers to the act of preventing, investigating, and punishing perceived offenses and crimes without legal authority." Fighting off one's rapist would count as prevention, and she did not possess legal authority to assault him while in his home. Then he sued her, forcing her to pay legal fees before dropping the case. What should Longhorn have done differently in this situation? At what point did she ever engage in "vigilantism"? His defamation suit against her is not due to a social media post, but rather her talking to coworkers and contacting authorities.
I'm not gonna straw-man you here, but you might want to think about the implications of calling what these women did "vigilantism" in light of the actual actions that they took. Namely, contacting the authories.
But let's leave the survivor's personal experiences aside for a minute and talk about systemic change. How should people who have been systematically abused by a system try to change it? Would revealing it's failures on social media for all to see perhaps be a step in that direction? It's not as if the levers of power that can make the changes you suggest are terribly accessible to the general population. If fact, they are far more accessible to the very people doing the raping, powerful men. Posting about rapists on social media is a tactic to change the justice system, it's just one that those currently priviledged by the system are threatened by.
Insisting that we must change the system, while decrying the powerless' efforts to do so, doen't that seem a bit contradictory?
To address your last sentence, we should give up on the so-called justice system. It does not create justice, but rather perpetuates inequality. Please understand, this does not come from a place of rejecting the concept of justice. On the contrary, I wish to see a more just world, and I am unwilling to compromise that ideal. The "justice system" is unjust. There are promising, proven alternatives. Why don't we try those instead of the promise of reforms that have never once materialized?