It might not be that Siva opposes the light.
Maybe it's just like the Vex. The Vex have the ability to simulate and predict their foes, but Osiris thinks that they cannot predict guardians because the light grants us "impossible" or "illegal" abilities.
Would technology be able to consume, enhance, and replicate a force they do not understand? Sure, the Iron Lords got Siva-fied, but possible it only happened after their ghosts where damaged/destroyed/killed.
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I like to think of the vex simulating x=1+2 and then al of the sudden 3 comes in shoots 1 and 2 and then steals x. we should be dead(thus eliminated from their equation) but we're not and then we shoot them.