The overall circumstances of the Nomar trade made it far, far, more polarizing to the fan base.
Not only was he still a fan favorite (though some of the shine had come off in the previous 2 years), but the Red Sox were A) coming off of a heartbreaking 2003; and B) were perceived to still be in the running for the AL East with the Yankees. It was inconceivable to a large percentage of the fanbase that trading away the team's third best hitter (in an era of Slugging Uber Alles) for light-hitting, defensive specialists at SS and 1B was somehow improving the team. People thought that the ownership group had gone fucking batshit, and the Red Sox were scuttling a chance at the playoffs in the middle of the season just to spite Nomar.
Yankees fans are "shocked" that the Red Sox are trading Lester? In 2004, Yankees fans were openly mocking Red Sox fans for the team trading away Nomar. "We would NEVER trade away Jeter! Your team will ALWAYS SUCK, and this is why!"
There's no comparison. Maybe the result of 2004 is clouding people's memory, but August 1, 2004 was a really dark and strange time for Red Sox fans. August 1, 2014 is just merely the sad aspect of doing business.
EDIT: people were calling for Theo's job after the Nomar trade (and if the Sox had lost in the playoffs again, he might have lost it).