The man only has one life so I wouldn't expect him to be trying to play a Bitcoin martyr. The feds are pro's at making people take deals they wouldn't normally take. The system is so rigged it it is not funny, especially if you don't have a great legal team and the money to pay them.. The fact that he pleads guilty is in many ways a win for the FEDS and a loss for the little guy who got caught in the wrong place and didn't know the right people.
IDK how much him fighting (successfully) the charges would help bitcoin. I think the case is really more about money laundering laws then anything else.
If anything, the case is about someone who did business and made money off the silk road site regardless of the morality of what was being done. I think the government wants to prosecute as many people who sold on silk road as possible to make others who sell/make money off other similar sites afraid to do business on those sites.