This really depends on how you define loss.
In a standard legitimate sale of a product, there is a bidirectional exchange of value -- the customer submits currency whose total value is equivalent to the value requested for the product being purchased. Simultaneously, for submitting the currency of that value, the customer receives a product of that value. (We'll assume the price is totally fair and equivalent to value at this point, but even if it's not the price presumably still includes the true value of the product, if not more)
In an illegitimate transaction -- literal theft, in this case -- the criminal customer forcibly receives the product, exchanging nothing of value in return to the merchant or the producer of the product. In this case, there is no question of loss; the customer has received something with inherent value and given no value.
In the illegitimate transaction of piracy, the end result is the same as theft with the sole exception that the original product has not been "lost" in the traditional sense of the word -- however, the criminal customer has still received a product of value and exchanged nothing at all, much less the value of the product.
Now, regardless of which of these three transactions has taken place for your product, I am presuming that your product had a significant cost to develop -- unless, of course, all of your tools were free, you had no expenses at all and you regard your time as totally worthless, in which case all income from the product is profit. I submit to you, then, that if your costs in developing your product surpass the value you received for it, yet the value you received for it is, itself, surpassed by the value of the product "in the wild" -- e.g. you have sold $450 worth of software, yet there are $750 worth of copies of it total being enjoyed by people (purchased & pirated combined) (100% arbitrary numbers), and the cost to develop the product was around $1500 -- then you have certainly incurred a loss on the sole basis that you have not received enough value to cover your costs.
The standard rebuttal to this is the tried-and-true "but they would not have purchased my product anyway." Perhaps this is true -- however, I would consider this irrelevant. Under normal, legitimate economic circumstances, the purchase of a product is the only way to attain it; therefore, if they would not have purchased the product anyway, they wouldn't have the product. In this case, they have not purchased the product, but they do have it and enjoy its use, and you have received no value in return for it despite having put value into it.
However, assuming the value received for the product exceeds the costs of producing it, but the value of the product "in the wild" as mentioned above still exceeds the value received... perhaps "loss" is less correct in this instance, but you are still lacking the total value that under normal circumstances you should have received. What would you call that?
In any case, I am not sure how it is fallacious to call a product of value obtained illegitimately (one way or another) for free a loss to the product's producer.
..and a user has never been entitled to the full enjoyment of a business's product. But it doesn't seem to stop articles like this from being written or large amounts of users to just steal it anyway.
I could hardly love this whole comment, but particularly that, any more. Rock on.