@@Wonderkid - AC
" Question is, how did this field become so obsessed with personal attacks as an MO? ..."
Ad hominem arguments are rife where substance is shy. Presently, the substance to AGW is extraordinarily shy. It consists of a laboratory fact some very pessimistic models and censored and manipulated data. Raw data has consistently failed to support AGW in any conspicuous fashion. Hansen's refusal to submit his data and methods to peer review is a fact rather than an ad hominem attack. It has been the single most important weapon in the so-called "sceptics" arsenal.
The failure to submit observations, adjusted data and methods and justification for the adjustments that have been used to reach a conclusion to peer review is a critical, extremely unscientific behaviour. It has also been called out by individual scientists who are convinced that there is at least a slight warming trend - up until about nine years anyway - and who cannot reconcile publicly-available observational data with with "adjusted data sets" and model forecasts which with respect to the publicly-available data have been abysimally poor performers.
So, the answer to your question is, again, where substance is shy or lacking, and where significance of results is equivocal, "ad hominem" attacks become common, because there is simply no substance to address, merely assertions. If you actually look at the debates regarding AGW, the ad hominem tends to be wheeled by the supporters. It is really irrelevant what your political or economic purposes are, IF your scientific work is honest and open. If your work is not open, and you refuse to counter your critics with openly debated data and methods, all you have left to fall back on IS ad hominem.
There are for example potential economic "biases," if you will, on both sides of the aisle. It is logical to suspect that any company dependent upon energy consumption might be prone to sacrifice long-term benefit for short-term profits. It is not nearly as often pointed out that the AGW proponents have made [financially] successful careers out of forecasting doom. And, regardless of how sincere they might have been initially, once data sets begin to be "adjusted" rather than models reformulated, well it no longer looks sincere, it looks desperate.
One of the important warnings the public should receive day is that "science" and "consensus" are unrelated concepts. Science attempts to address knowledge. Consensus is a political term and is both irrelevant and meaningless in science. For instance, prior to the development of plate tectonics, the consensus in geology of how mountain ranges came to be was an absurd, oxymoronic conjecture that had profound problems with thermodynamics, never the less, it WAS the consensus - for decades.
One of the most disturbing aspects of this debate is the harm the falsification of AGW would bring to us socially, economically, and biologically. The proposed counter measures for AGW - reductions of emissions, energy efficiency, alternatives to oil and coal, etc. - are ALL beneficial actions economically and scientifically. Because of the politicization of the argument, it has moved outside the appropriate venues of scientific debate and into public, in congresses and parliaments. Critical research funding for alternative energy, ecological research, engineering, etc., could be lost, all because AGW proponents refused to be open and politicized a debate that should have received decades of study before the public was exposed to it in any serious manner. Even our politics could benefit; consider western involvement in the Middle east if we had no concerns to keep oil flowing. Only religious fanatics would have any political interests there.