The primary cause of speculation, suspicion, and general lack of sympathy for the man is the timing of his diagnosis(within a day or two of exhausting his last legal option) and that it is being used as an attempt to prevent extradition.
But, giving him the benefit of the doubt and supposing that he legitimately has Asperger syndrome let us examine what this means.
Asperger syndrome is a very, very, high functional form of autism, at least by some classifications as it is so new there is some debate how to classify it. Some in fact suggested that Asperger syndrome is less a human "disability" and more a human "difference."
But bypassing that debate, its primary symptoms are awkward social behavior(chiefly caused by not recognizing non-verbal communication), clumsiness, and obsession over patterns of behavior or subjects of interest such as refusal to change a routine or an intensive love of a hobby (see
http
/www.udel.edu/bkirby/asperger/aswhatisit.html ).
Typically, someone with Asperger syndrome can learn and adapt to compensate for these short comings and live a normal though socially challenging life(see
http
/www.ninds.nih.gov/disorders/asperger/detail_asperger.htm ).
Of particular note, Aspergers syndrome is not characteristic of impaired cognitive nor typically of speech functions. So Gary McKinnon is in a sound state of mind and able to, at least verbally, communicate effectively. It doesn't really sound, to me at least, like Asperger syndrome renders someone in a highly delicate state of being or unable to be held accountable for their actions.
Sympathy for Mr. McKinnon is further dampened when research turns up that(according to his lawyer) "In 2003 McKinnon rejected a written plea offer that would have given him six months to a year in a U.S. low security prison, followed by a transfer back to the UK for parole six months later"(see
http
/blog.wired.com/27bstroke6/2008/08/uk-hacker-gary.html and
http
/blog.wired.com/27bstroke6/2008/07/british-ufo-hac.html ).
Of particular note is the way the whole affair is pitched by most news agencies, who report that he faces between 60 years to life in Gitmo(typically) after being tried in military court as a terrorist.
In reality, he would be tried in two civilian courts based on the states where the computers he hacked were located. Depending the monetary damage he is convicted of doing he could spend from six months to 6 and a half years in a civilian prison.
Now, to top it off, he apparently did all of this because he was looking for evidence of UFO's. He claims to have found weak circumstantial evidence to support his claim but was cut off in the process of retrieving it(see
http
/www.wired.com/techbiz/it/news/2006/06/71182 ).
My impression of the man so far is he is a weaselly quack and I(and I imagine others as well) have trouble sympathizing with him because of this.