What NGTM-1R said. One shot from a GARDIAN laser won't kill a fighter, but it will damage it enough to make it fly home for repairs. Fighter combat in ME works by throwing wave after wave of mass torpedoes and fighters at point defenses to make them ineffective. That being said, the Codex does mention Interceptors specialized for anti-fighter duties. ME2 also introduces that fancy silaris armor that's made out of diamond and carbon nanotubes and which is mentioned specifically in the codex as being too expensive for anything but fighters, so with a little judicious handwaving fighters could survive long enough to be useful, especially if the player is going up against targets besides dreadnoughts and carriers, like Terminus raiders or Batarian slavers. There's a few months between ME2 and ME3 so there's time there to do a small campaign.
