It's reasonable to discuss catastrophy when it's a possibility of the current trends, albeit perhaps unlikely.
If you look at sites trying to keep the discussion in the scope of scientific discourse, there is actually little alarmisim occuring. I challenge someone to show such, in articles or unmoderated comments, from RealClimate.org.
Compare this to groups and commentors that like to claim cretainty that there is no cause for concern, or even interest in the matter by most people.