I'm also in the camp of believing that Sandy Leon should go. I wouldn't hesitate to release/trade Leon and give the backup C job to Swihart. I would certainly do that before trading Swihart for nothing. True, maybe I'll change my mind if I watch Swihart behind the dish for an extended period of games, and maybe I'll reach the same conclusion the Red Sox have seemed to reach regarding Swihart's defensive skills, but I'm not there yet. Moreover, the Red Sox have a defensive catcher in Vazquez, they can afford a less efficient defensive catcher behind Vazquez with the hope that Swihart can develop as a hitter and add a little offense to the lineup.
What's the worse that could happen? You release/trade a fringy Sandy Leon and give Swihart an opportunity at C. If it doesn't work out, you trade Swihart and find a no hit defensive catcher somewhere to backup Vazquez. Thus, if this scenario plays out, you've lost Sandy Leon and maybe can't get him back. If that happens, so what? The Red Sox aren't going to win the World Series this year because they dumped Sandy Leon?