Tone is nearly always a bullshit argument used to dismiss the content of what's said without addressing it.

Good communicators don't worry about it too much because there are lots of reasons someone can take a certain tone - for example if they're tired or stressed! So they just make sure they understand what the person is conveying without worrying about how it's conveyed.

Someone who focuses much on tone is likely a poor communicator themselves, or frequently just trying to be manipulative.