I believe a claim that someone is tone policing is only valid when the substance of the message is ignored due to superficial claims about the way the message was delivered.
So when someone says:
It’s bullshit that women get hassled online so much.
And the reply is
How dare you say bullshit! What kind of person uses language like that! My goodness gracious, fetch me my fainting couch as quickly as possible, I do believe seeing these terrible words on my screen has made me light-headed!
That is ignoring the content of the message, in favor of commenting on superficial aspects of the message, and derailing the discussion into meta (discussion about the discussion) in the process. I consider that a valid use of the tone policing argument. But the tone can be adjusted, without falling into that trap:
Yes, there’s a lot of data to support the claim that women get hassled online a lot more than men, and it is unfortunate. Also, be aware that we don’t allow profanity per our site guidelines, so I’ve edited out that particular part of your message. Please continue the discussion.
This does not mean that stuff you would normally not allow – cruelty, profanity, personal attacks, and so on – should suddenly be allowed if they are presented under the banner of a righteous moral cause. In other words, these two statements are not equivalent:
Hi Bob, I’d agree with your point A, but your point B contradicts C and D, which I outlined above. How can you reconcile the two?
and
Hey Bob-a-job, you f**kstick, can you even F**KING READ you idiot? Did your mum drop you on your head as a f**ing baby? You’ve totally ignored points C and D. Your whole argument is f**ing WORTHLESS. Srsly. People like you are the reason the world is so F**ED UP.
TL;DR a tone policing claim is only valid, in my opinion, when someone is ignoring the content of a message in favor of focusing on relatively superficial aspects of how the message is delivered. However, this does not mean that delivery is always superficial, that you are free to deliver a morally righteous message in any form you like, no matter how cruel.
How you say something is just as important as what you say. Be angry, that’s fine, just don’t let your anger drive you to lash out and hurt other people.