All the people saying "Why do we need this, this is dishonest and it won't do anything and anyone offended by these words should just grow a thicker skin" need to tell me- what would be so horrible about people NOT using racial slurs in the course of videogame chat?
What would we lose? What specifically would signing up to this little pledge forbid you from doing that is so very important? You can still insult people. You can call them fuckfaces, assholes, human waste product, shitstains on the heel of society, you can imply that you're having sex with their mother right now, or that you did the night before, or possibly are going to in the future. You can ask spawn campers what they learned in the 3rd grade today. (Well, it's summer, but you get the idea.)
The range of personal insults is so vast that not using race, gender, sexuality, or disability doesn't even cut out 1% of what you can potentially say.
And if you're not using those words already, you lose even less. You lose nothing. Nobody's freedom of speech is being threatened, there's no great art being endangered by this.
Why do you panic so?