Then if you must, you might want to choose examples that don't shoot your point down. For anyone who hasn't read the Silmarillion and The History of Middle-earth, the Valar did not intervene specifically because their overwhelming power risked far greater harm than good. The last time they directly acted against Morgoth, Sauron's master, they sank half a continent. Tolkien explicitly points this out and that they DID act by sending the Wizards. Trying to claim they sat on their duffs is completely ignoring that.
Meanwhile, there is exactly zero reason beyond But Thou Must! that we don't just kill the warlocks powering the portal. Sure, "choosing to sit on your ass and not answer the call to adventure in a fantasy context is pointless". No problem there. The problem is that the Dark Portal event only works if the PC is a complete moron and Khadgar too.
"Hi, I'm Khadgar, I was deeply involved with the events of WC1 and 2, know damn well who Gul'dan is, know damn well how Dark Portals work, but screw it, I'm not going to bother dealing personally with shutting down this Dark Portal." Hey, the portal is being created by channeling power through these warlocks, who are canonically anathema to everyone else. Let's just let them go their merry way. A slight tweak such that we accidentally freed them would have been worlds better, something like a booby trap laid by the Iron Horde, since they were expecting us.
Your defense of the Dark Portal events in WoD revolves around speculation. "Maybe they didn't know", "maybe they thought those people might be different", and maybe pure speculation with nothing to back it.
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For the same reason that you don't compare Mozart and Justin Beiber.
Sure, Tolkien has errors and inconsistencies, largely due to two things:
1) Writing over years if not decades.
2) Perfectionism such that he'd be unhappy with something and revise it.
When he realized he'd made errors, he either corrected them or created something better, such two of Glorfindel leading to an entire structure of how Elves could reincarnate.
Trying to list such errors is nothing more than deflection from your flawed comparison. The Valar had explicitly spelled out reasons not to intervene directly and did so indirectly. We had exactly no reason whatsoever not to kill Gul'dan while he was a portal conduit.