I feel like a lot of dissent around the GPL stems from two places: corporate entities, and other organizations that have a different interpretation of software freedom (BSD, for example).

In the case of BSD, I think there is some discomfort around the idea of the GPL's viral nature, eg, if you write something that interfaces with GPL software or otherwise relies on a GPL library, that the new software being written will have to abide by the same licensing as the software you're interfacing with, or the libraries you're building on. From some points of view, this could be seen as problematic.