Oh I know that they were not at all useful in the way they were "intended." You pretty much get that vibe from Izual when you set him free. Well, that and all the events of Diablo I and II in general. Also leads to the question of why Baal wants his "broken" soul stone if he was free. You likely could argue there was still power of his in it, and also that it isn't ever found, but who knows how that is going to work out. I just can't figure out any good reason, and there doesn't seem to be any explanation, that you would want to destroy them.
I have always been curious about something, maybe it was answered in this thread and I didn't get it, but I still have the question all the same. The soul stones were originally given to the Horadrim to contain the Prime Evils as they were banished to Sanctuary correct? What point was there to actually destroying them? You are just removing their prison. I thought that perhaps this banishes them back to the burning hells, but as they are banished would it really? This would work all well and good if they actually were banished back, but now that the worldstone is destroyed there would be little stopping them from just walking back in. Black soulstone I got nothing so not even trying there.
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