Question about the LMB and ICM

How does the Lightmass bomb work? Does it target just the locusts or can it wipe out anything?

Why does the ICM kill locusts as well? Is it possible to be partially infected with imulsion and if so does that mean the machine wiped out humans to that hadnt turned fully?

Or are locusts inherently infected since they are born from infected humans originally?

BONUS question. Why was it exactly why Adam Fenix was upset at the end of Gears 2, he mentioned that sinking it was a good idea yet after the credits he was unhappy, with what exactly?