It's rude, sure, but I still fail to see how that rises to the level of attack? What harm is intended or possible from a comment like that? Are all rude comments attacks?
Accusing someone of having blood on their hands is generally an attack to mean that the accused has caused unjustifiable death. To contrast, if person A saves person B from a mass shooter by killing said shooter, it'd be odd for person B to say to A "You have blood on your hands!" (unless it's literally true).
"You have committed unjustifiable harm." is clearly an attack. People who commit unjustifiable harm are generally supposed to be shunned, penalized, or killed according to how human societies have operated across the world (various things can get in the way of this, but this is the baseline).
So now we're at "My employer's client is someone who should be shunned, penalized, or killed. (and I'm going to post it publicly in a way to make it possible for said client to be able to see it!)".
Finally, a lot of business runs on vibes. Having employees that attack your clients in public sends bad vibes. Even if it's just a 'rude comment', why endanger your business for someone who so deeply fails the vibe check?
