We're not talking about Coke taking market share from Pepsi, which is analogy I saw elsewhere. A better analogy would be Company A that doubles its own profit by, say, destroying the public shared water source 5 other companies rely on, with total profits 10x the extra profits for Company A. So the overall portfolio effect of the actions is very negative.
For many years, economists have just sort of accepted that externalities are a thing, and are bad, and there is not much you can do about them. By definition, you can't hold companies accountable for these costs. If you could, they would not be externalities. This suit is trying a new legal theory to change that.
IANAL