While yes, in a perfect world, a good argument should stand by itself, this is not a perfect world. I would agree that dustin's debate skills could use some serious refining, however the crux of your disagreement seems to lie in the interpretation of his evidence. You argue that the CO2 charts he is using cannot be extrapolated in a linear manner over a period of hundreds of years while he says that they can. Since no one has provided documentation either way (only grossly misunderstood metaphors), it comes down to who should one believe. Thus, I would say that at this point, academic credentials are relavent to the discussion unless one of you can site a paper that explains why those graphs are valid under current models for x number of years.
Dustin's graph extrapolation relies on his extending the lines as a current trend for an indefinite amount of time, with his assumption that this can be done infinitely (or at least to a time in the far, far future of his choosing). This assumes that CO2 levels will continue indefinitely and / or that there are no negative feedback mechanisms, only positive ones. It doesn't take an expert in global environment studies to see the flaw in this.
CO2 levels aren't endless. Furthermore, the CO2 we're releasing is in the form of fossil fuels, and of those, only the fossil fuels we are able to access directly and convert. So there is a finite level of CO2 that can be placed into the atmosphere. For Dustin to make the claim that this level is sufficient to create a Venus-like environment, he must demonstrate that with evidence.
Secondly, our oceans are great stablising force when it comes to temperatures and atmospheric gas ratios. This comes at a cost; variations across the globe in terms of climate and local weather patterns are extremely susceptible to changes in oceanic currents, affected by haloclines (salt differences) and thermoclines (temperature differences). Furthermore, while the ocean can suck up a lot of CO2, this does make it more acidic, making it difficult for calcium-shelled animals to retain their shell's integrity, inevitably killing them.
None-the-less, the impact of our global water bodies on warming is to be taken into account. I don't deny global warming and great changes in weather patterns, yet considering we are vastly different to Venus in chemical composition, position in the solar system (much further away from the sun than Venus), and climactic feedback mechanisms, it is up to Dustin to demonstrate sufficient similarity to argue that we will also achieve a runaway greenhouse effect.
The awful thing is that he might indeed be correct. Give the evidence, I might agree. If Dustin had expertise, he would see the need for evidence beyond a graph. But Dustin has no evidence, he argues emotively and passionately, but insensibly. Sadly, it's his kind who detracts from the climate debate.
Athon