First of all, there has to be some sense of objectivity when discussing this. It goes without saying that the consumers who gain an unfair advantage by using these services would like them to be kept that way (at least that would be the initial response from most).
Since this community is based around software and games, I will keep to those and stay away from digital music downloads.
I sincerely enjoy the term "international protectionism". Normally the infant industry argument is applied on a nation- or region-level. However, for two main reasons taxing digital goods will be difficult: firstly, as noted above, an uneven legislated taxation will simply "push around" the affected companies, and the different legislators will end up competing with each other. While this may not necessarily be a bad thing, it does mean that the development of an international tax level will be significantly slowed unless action is taken on an international level. And secondly, taxing digital goods is hard because it doesn't pass customs (you can't easily measure it) and the VAT is usually charged based on the location of the buyer, not the seller. The international protectionism is enforced on an international level, and anyone who wishes to change that without the consent of everyone else in the world, will in fact end up losing in the long run (at least theoretically) as companies adapt to the local taxation higher than their near and far neighbours.
Producers are taking this into their own hand, and going over the head of the retailers. Impulse and EA are perfect examples of this. They sell through normal stores, but also present the digital goods on their own. Where the producer does not make a digital version available, subretailers take the matter into their own hand and sell cdkeys on the internet(s). Thus, whether or not producers choose to sell digital versions, they are available on the market. Taxing digital goods will hit every producer. The question here is who of the suppliers it will affect, because that is where the unfair advantage lies. Right now, the taxation system favors digital goods. Anyone who supplies digital goods will therefore be hit (this is obvious) while physical retailers will only be hit indirectly as turnover for producers decrease (physical retailers would still benefit overall due to rules of substitution - at least, that is the logical conclusion). Of course they are not always separate, for example GAME (game.co.uk + local versions) supply both digital and physical sales, but it would still apply to internal divisions).
Does the infant industry argument apply to digital goods? This is the fundamental question that has to be answered. If the argument applies, the taxation should not be placed. If it doesn't apply, then the taxation should be placed (although it may not be beneficial to individual regions). My conclusion is that the argument no longer applies. This is based on three pieces of vital information.
1) New titles are consistently sold digitally, it is no longer a fringe supplier industry. As noted above, almost every game can now be bought digitally.
2) The digital supplier industry is seeing consistant and large increase in sales and customers, both in relative and absolute terms. We all remember Steams announcement that they had reached 15 million users. If my memory does not fail me, frogboy commented on these forums that we (the forum users) seriously underestimated their sales through impulse.
3) Digital goods are now being sold by traditional online stores who used to deal primarily with taking orders through their sites and then sending the physical package by snail mail. Amazon is a prime example of that.
These 3 things put togheter means that the movement towards serving digital goods is happening where it hasn't happened already. Frankly, the infant industry argument cannot possibly apply any longer, when major suppliers such as EA and Amazon are seriously involved, and suppliers who specialize in digital goods have been proven profitable. Furthermore, the market is growing, and while taxation will certainly hamper the growth, it is a fair assumption that it will continue to grow or at least certainly not shrink.
Edit: It should be noted that taxation has already started happening on digital goods. North Carolina is by no definition "first".