I think the point of Earth day is to provide information/awareness/action to "save the planet" (aka reduce pollution and the human footprint we're leaving). It should really be called "save the human race day", because the Earth is just fine.
People don't destroy the planet because they are unaware of the damage they do.
Also, Earth is not just fine. What is earth? It is the blue planet. But a severe atmosphere transformation is possible and it could change this. Sure, the planet would remain, but it could become inhospitable for any advanced life and change appearance completely. Basically become the younger sister of Venus, where no liquid water exists anymore and temperature is uniform around the globe because of the thick isolating atmosphere.
Venus is still pretty damn fine as a planet.
Not really. You do like xkcd, don't you: http://what-if.xkcd.com/30/