3) Damage - To apply the word damage means that something is out of norms. Consider the planet has been both hotter and colder then it is today...I say that no 'damage' has occurred...
Earth used to be a rock without an atmosphere a few billion years ago, do you believe it is right for humans to intervene if we were going back to that state? Would it be fun to turn Earth into a Venus with 400 Celsius temperatures, after all you'd get one hell of a suntan!
2) Irreversible - Once again, see above...the planet has been on both ends of the spectrium and, if you look out a window today, it has reversed
True but the existance of 6 billion humans on this planet is also reversible, especially because we need stable food supply and crops need stable climate. Servers need electricity, suppose all electricity in the USA was shut down - the entire grid including all backup generators, would the Internet survive? No, the Internet would die. Yes, the Internet would END, Google would go BANKRUPT, SLASHDOT.ORG would END, all posts would be DELETED. Affecting the climate is the same as sending a ten gigavolt power surge down the grid for 5 years, all servers would burn out in a few seconds. What if the grid randomly varied the voltage between 1 volt and 10 Gigavolts, no server or DNS server or DNS root server would survive.
1) Unnatural - What the hell gives them the right to decide what is natural or unnatural? Thew world has been MUCH MUCH hotter and MUCH MUCH colder then it is today. So where do you draw the line between natural and unnatural?
I would define unnatural as mass extinction. Would you like to try mass extinction? Go and live in the Sahara desert for 3 months, you'll be dead within a few hours.