If you are even remotely paying attention while playing ME2, you can't get Garrus killed unless you deliberately set him up to die. In which case... congratulations, you just screwed yourself out of a companion and female LI for ME3, should people now be rewarded for killing off characters deliberately?
But you can't romance Garrus in ME3 without an imported romance from ME2. So it's not just the matter of keeping him alive, you have to romance him too!
Did BW think femShep players were going to be that clairvoyant and romance Garrus while keeping Kaidan alive? Were they supposed to know Jacob would cheat or Thane would die that early or without acknowlegment?
If Garrus was available from the start of ME3, it would have helped.