I wonder,,,,, are the infected sentient? are they able to shoot guns and stuff? [probably when theyre first infected yes,] I'd assume on later stages they wouldn't be able to be, *shrug* [so I know what zusat may be walking in to.]
Think of the enemy not as completely brain-dead monsters, but more as people with absolutely no moral compass and only a desire to kill and destroy. They lose the ability to use most advanced machinery and tools beyond basic weapons, but can still use their basic firearms (even if their aim isnt too good) and how to manipulate incredibly simple tools.
Same with the boss force-users. They will be able to use their lightsabers, but any force abilities beyond the most basic/instinctive ones will be lost to them.
For my last post, it was a bit long so I split the two sides into two posts this time.