In the case of Calibre, has Kovid even acknowledged the existence of Alf? If he hasn't, I can't see how it would be considered as a nitpick. He has created a piece of software that allows extensions. It isn't terribly different than Linux, OS X, or Windows being able to run software developed by a third party. (Doesn't Alf contain a standalone program in addition to the plugin?)

That said, it would be interesting to find out how Alf is used. Judging from the comments on this forum, its primary uses seem to fall into two camps: those who want to do format conversion in order to buy from one vendor and use an ereader from another vendor, as well as by those who have a general distrust of DRM. Neither imply copyright infringement in the sense of distributing copies to other people, even though it is probably copyright infringement in a legal sense. It also makes sense that copyright infringement wouldn't be the primary use of these tools. It seems as though very few people are actually interested in the distribution end of piracy, where DRM removal is necessary. Most of those who do pirate seem to be interested in getting free stuff. You don't need DRM removal tools for that.

As for suing under the DMCA, why does fjtorres think that publishers want to avoid opening that can of worms? Does it have a chance of failing under a constitutional challenge? Or would there be (more) public pressure to repeal the legislation?