I'm smart enough to know this most likely won't change anything but hopefully, this could get Disney to realize the mistake they made and not do it again in the future.
I agree on the point that if people say a bunch of stupid shit while working for a studio, the studio has full right to fire him over the possible controversy. This situation is very different though as he made these jokes years before he was working for Disney and also the fact that they were jokes. I agree with most, including Gunn himself that the jokes were shitty and un-funny but they were still jokes, it wasn't an opinion or a statement, it was just a bad attempt at being funny.
The other thing is if you do this to Gunn you have to do it for all the other directors who have said some crappy joke sometime in their life, which is all of them, cause I doubt there's one human on this planet who hasn't made a shitty joke once or twice in there life.
If Marvel would come to their senses and re-hire Gunn that would be great but if all we can do is have proof by your signatures that Disney made a mistake i would still count that as a win.