You're telling me that Joss never received hate mails, letters, messages, etc. before? Any public figure can be the subject of criticism. I think he took it a little too seriously.
Anybody who tells someone to go kill himself should lose all credibility instantly. I get that some people were angry that Black Widow didn't have the role they expected, but this isn't the first time - nor will it be the last time - that a beloved character in a movie is handled a way some of the fanbase doesn't like. That's why it's called an interpretation. If they aren't happy with how Joss wrote their favorite character, they can simply choose not to watch the next movie.