

Because the inverse of that is how people get conned. Someone blowing absolute smoke with a confident tone and a sweet word. Tone is about the worst indicator of trustworthiness
Sure, skilled sociopaths con their way up that way, or that’s how soulless marketers manipulate the populace. However, that does not mean that most people who are kind are sociopaths or soulless. On average kind people are just being kind.
Subjective. “A toxic person is anyone whose behavior upsets you and adds negativity to your life.”
Asking a simple question and out of the blue getting a response intermixed with full caps and “fucking” would be enough to add negativity to many if not most people’s lives. Also the unyielding need to defend one’s doing so doesn’t help to convey the converse.
You “inform” them afterwards, therefore they didn’t know.
Not sure what the definition of “language policing” is, but welcome to the Internet. You’re free to be crude or toxic while others are free to point out it out, which is rarely needless.