Here's some things to consider:
No other team ever made Damon an offer besides the Yankees and Red Sox.
Damon said he would take a "home town discount" if it was put on the table prior to 2005. It wasn't. So he said, at the start of 2005, that he would not take a home town discount and fans knew this going into the season and going into free agency. It is a very strict policy on the part of the new ownership and Theo that they do not negotiate during the season (as it is with Cashman and the Yankees for the most part, which is why Sheffield wasn't happy at the beginning of this season).
The Red Sox "negotiated" with Damon without Theo. Their tactics didn't seem as, well, good as Theo's would have been. A big reason they brought him back in my opinion. Instead of offering him the most they were willing to pay him up front they "insulted" Damon with a very low ball offer, an offer everyone knew cold and would be outdone by just about any other team, especially the Yankees. It is widely thought that if they had given their "final offer" first he would have accepted it, which is the way Theo usually works.
Damon isn't worth the contract he agreed to on the field. At least, he probably won't be. Not that it matters really. But the fact is, the Red Sox, as "rich" as they are, aren't the Yankees. They aren't willing to throw around millions upon millions of dollars for a player they don't feel is worth those extra few million. And last time I checked, a few millions dollars is a lot of money, no matter who you are. Damon is by no means a "victim" but he was on the end of some bad negotiating. Damon as marketed himself very well over the past few years. He, along with Papi, Manny, Pedro, V-Tek, and others have helped put fans in the seats, helped sell millions upon millions of dollars worth of merchandise, and has been a face of the franchise for about 3-4 years.
And the biggest argument you'll hear is this: without Damon in 2004 the streak continues and this year would be 88 years. I don't know for certain, but as a Red Sox fan who was lucky enough to witness A-Rod's home run ball being tossed back over the monster , just to have Damon throw it right back over (and have it tossed back again after that), dave Robert's stolen base in the 9th inning, and Papi's home run to win it and turn the series around during Game 4 of the ALCS in 2004, I'd be a completely different fan right now.
I'm not saying cheer him, but he's no Roger Clemens. Don't boo him.