User blog comment:Tali's no.1 fan/Shepard or Sam Fisher?/@comment-2130363-20110528030951/@comment-743796-20110601114526

But Fisher was also a double agent (per the game Splinter Cell: Double Agent) and thus was killing people on both sides for most of that game. Shepard only killed enemies, and although not a double agent, he was loyal to the Alliance despite working with Cerberus in ME2.