Regardless of whether you think the Red Sox *should* have traded Marco Scutaro for the cap space or not, you have to admit that this is a staggeringly weak return for a player who has (a) performed very well at a scarce position and (b) has a very reasonable, short-term contract. Mortensen is a *bad* baseball player, one who is worse than most of the spaghetti we already have and has limited upside. You'd think a well above-average SS like Scutaro on a reasonable contract could get you something of value.

I don't think you understand. Even evaluating this deal in context, it makes no sense for three reasons:
a) Even if Scutaro's salary could be better allocated to Oswalt/Cody Ross/etc, this team should have gotten a better return for a well above-average player in Scutaro. A well above-average middle infielder on a decent contract should fetch more than a replacement-level player. This is virtually uncontestable-- Scutaro had vastly more trade value than Mortensen, and it's not *at all* close. One could argue that the trade market dried up, but I think it is a lack of due dilligence from the FO. Let's look at comparables:

Rafael Furcal got traded during the 2011 season and while the trade was admittedly midseason (when prices are inflated), the impending free agent Furcal was (a) more injury prone, (b) only available for half a season, and (c) a comparable player on the field (Furcal had a truly atrocious beginning to 2011 with a .516 OPS at the time of the trade, but had a history of good contact rates and defense). The return was Alex Castellanos, an outfielder who hit .322/.406/.603 as a 25-year-old in AA. Admittedly, Castellanos has poor plate discipline (bad K/BB numbers) but projects to be a 4th outfielder/right-handed half of a platoon with good power and a bit of speed.

Clint Barmes, an all-glove/no-bat SS/2B (averaged about 1.5 WAR the three seasons before his trade), was traded from the Rockies to the Astros during the 2010 offseason for Felipe Paulino. Barmes was again an impending free agent prior to his trade and was due $3.9m for the 2011 season. Again, a cheaper contract, but for a much worse player than Scutaro. The return, Paulino, was a young and inconsistent starter but one who possessed a 95.1 mph fastball who had put up decent K and BB rates the two years before-- a real asset with tons of upside (who in 2011 put up 139 innings of 3.73 xFIP ball).

Hell, even Mike Aviles-- a worse player than Scutaro in every aspect of the game, albeit with a substantially cheaper contract and under team control for a few more years-- got traded mid-season for Yamaico Navarro, a useful future IF with decent pop and defense.

Note that all of these returns were *substantially* better than what the Red Sox got back for Scutaro, and it isn't even close. This team should have at least gotten back some sort of asset rather than a 27-year-old replacement-level AAA player (but one with an option left!).

b) Oswalt/Ross/etc. have yet to be signed and it doesn't look like a signing is imminent. If, say, the team had effectively already agreed to terms with Oswalt and was scrambling to find someone to take Scutaro's contract so they could finalize the Oswalt signing, then maybe this deal wouldn't look so bad. As it is, there is no guarantee that the Oswalt signing *does* go through.

c) This trade reeks of poor planning by the ownership/FO. If they knew this team would be right up against the salary cap and would struggle to acquire the necessary pitching, they should have prepared better and earlier by either (a) dealing Scutaro earlier in the offseason or at least opening up the bidding so that you'd be able to get more of a return (and potentially keeping Lowrie as a cost-effective, skilled replacement instead of the Punto/Aviles platoon) or (b) not offering Ortiz arbitration (as suggested by Yirm earlier in the thread). That they waited this late in the offseason to unload salary speaks to poor big-picture planning/communication between the FO and the ownership earlier in the offseason.