Ok a quick thought, why havent any of earths ships got Goa'uld tech on them?
They could easily implement the Goa'uld Projectiles (considering the majority of human ship systems operate on crystal tech) and the information and source material is easily accessable, you can get an Alkesh on the galactic black market, i dont see the problem, surely the SGC can cannabilise parts from Goa'uld ships.
Or ask the Jaffa or the Tokra to help them. So why do they stick with human missles, which deplete and are rather inaffective against any shielded target. I understand the rail guns (anti fighter/missle capabilitys) But why not build in Goa'uld energy projectiles?!