Your argument only works if technical restraints are (a) necessary and (b) effective. If they’re not necessary, i.e. rightsholders can profit without needing to “enforce their rights” either legally or technically, then the limited effectiveness of lawsuits against individuals is not the end of the world. (This doesn’t contradict a belief that legal relief should be available in principle, and in any case, it is available in practice against large-scale or commercial operations.) On the other hand, if technical restraints aren’t effective, then rightsholders gain little by imposing them, and lose little by removing them. Thus, even under the assumption that piracy is a huge cost and can’t be solved without technical restraints, it wouldn’t be inconsistent to advocate banning them, because piracy couldn’t be solved with them either!
In fact, there’s a good argument that DRM is neither necessary nor effective: the former as demonstrated by the music industry, the latter as demonstrated by the movie industry (where the availability of new releases on torrent sites is a matter of course, as it has been for many years). True, it’s more complicated than that, as both technical and market factors greatly affect the utility of DRM in any specific situation. But as a general principle…
In fact, there’s a good argument that DRM is neither necessary nor effective: the former as demonstrated by the music industry, the latter as demonstrated by the movie industry (where the availability of new releases on torrent sites is a matter of course, as it has been for many years). True, it’s more complicated than that, as both technical and market factors greatly affect the utility of DRM in any specific situation. But as a general principle…