This should be in the FMP thread, I think.
And it really is a 'you' problem. Among the starter weapons, at least the following weapons are able to harm Silacoids: Stun Rod, HMG, Sniper Rifle, Large Rocket, High Explosive, AP Mine. Several of these are non-"explosives-shooting". The miniguns might not work immediately, but they strip armour even when doing no damage. Tanks also work, as you said yourself.
Even Rifles might work occasionally when rolling high, since 50 < 2*30. So will hand grenades that land in the exact same tile.
Basically, the mod is not to meant to be played with an "I will faceroll every enemy regardless of my weapon choices" mindset.