I think that people frequently say a vague or rounded-off or approximate thing, and then other people frequently step in to try to clarify, and this attempt at clarification often ends up making things worse.
My go-to canonical example here is something like a teacher, in the middle of trying to mete out appropriate consequences to a bully. You can imagine an onlooker seeing the bully getting punished saying something like “but wait—the other guy threw a punch, too!”
This reads, to me, as a basically-prosocial attempt to make sure that relevant detail isn’t lost! “Both guys were punching.” The onlooker saw the teacher responding as if only one bad thing happened, and wanted to make sure that everyone understood that at least two bad things happened. Ten points to Hufflepuff.
But in my culture, there are few things you can say that are as scary and dangerous as “both of you were wrong” or “both of you did badly here” without a follow-up to offer detail. Responding to one person receiving a punishment with “wait, both guys were punching, though,” is, in context, a pretty clear bid for something like equal punishment. And it’s fairly rare that two people were anything like “approximately equally in the wrong”!
Indeed, if a bully is tormenting a victim, and the victim kicks the bully in the shins, both people were in violation of standards of good conduct.
But to wash away the distinction between “this is unjustified, though understandable” and “this is unjustified, period” is really, really bad. It’s sort of a fallacy-of-the-grey—by emphasizing the true fact of everyone’s nonzero transgression, you make it harder, not easier, to keep track of extremely critical information about which behavior was worse.
In my culture, the correct move is to make a single, complex statement that includes “what A did was bad in this way, and what B did was bad in that way, and we weight those two badnesses thusly.” If what we really mean is something like “okay, but was the other guy’s conduct completely appropriate, or did he, too, do something at least a little bit wrong?” then we would ask the teacher something like “but wait—even though the first guy started it, isn’t it bad that the other guy hit back?”
(To which the teacher could respond with whatever their philosophy of game theory and retaliation has to offer on the question.)
Anything else ultimately ends up being a gift to the person with the more problematic behavior (and what is incentivized tends to then happen more often). It also ends up being a punishment to the person who was less-in-violation (which can discourage them from even bothering to try, in the future, and encourage them to instead ramp all the way up as fast as possible). I think it’s important not to chime in with “wait, but both of them were doing it, though,” unless you actually mean “…to roughly equal extents, such that they’re roughly equally culpable.”
In practice, I think the crowd does leap to that second, implied meaning, unless you explicitly rule it out. So if it would be bad to imply it, then it’s bad to stop there.
FOOTNOTE: This dynamic has a cousin, which is something like “well, we only openly criticized the person who was doing something a little bit wrong, because the person who was doing something outrageously, egregiously wrong is obviously beyond saving and wouldn’t listen anyway; we spent our points where we thought they had a chance of accomplishing something.”
But that subtext often doesn’t carry! Instead, the message that gets sent is “the guy who said ‘kill yourself’ did literally nothing wrong and the guy who replied ‘hey, fuck you’ deserves two paragraphs of censure and criticism.”
If you come out of the woodwork to heavily criticize exactly one party in a conflict, this sends the message that exactly one party in the conflict deserved criticism. If what you actually want to convey is “I’m going to speak to the person who’s potentially reachable/saveable and worth talking to, and I’m going to ignore the troll whose behavior was even worse,” you gotta say that part out loud.
The world isn't black and white, but it's even dumber to think that it's all just one shade of gray.