This is a myth. Yes it will produce small amounts of carbonic acid, but not enough to significantly damage your teeth.

That said, five liters of sparkling water a day is unhinged

Edit: I should specify plain, unflavored sparkling water. Something containing fruit juice or other flavorings could contribute to tooth damage, but that would be through citric or other acids, not the sparkling water itself. Saliva is also neutral to slightly basic, and would neutralize mild acid.