While I agree Lego will most likely never do stuff like HALO and Starcraft/Warcraft, it is not for the reason you give. Lego does make guns. They make several as a matter of fact.
To quote the link you gave:
The basic aim is to avoid realistic weapons and military equipment that children may recognize from hot spots around the world and to refrain from showing violent or frightening situations when communicating about LEGO products. At the same time, the purpose is for the LEGO brand not to be associated with issues that glorify conflicts and unethical or harmful behavior.
So they want to avoid doing an AK 47 or an M4 Carbine. They also want to avoid anything that seems to glorify conflict, like HALO and Starcraft/Warcraft.