To take this out of the academic realm and into the real-life realm: I've actually done projects for companies which have corporate policies disallowing the usage of any copyleft licenses in their toolset. My use case was a web application, which would not have been affected by a GPL library usage since we were not distributing binaries. Nonetheless, those clients would not have allowed usage of any such libraries. You can argue whether or not this is a good decision on their part, but I don't think the companies I interacted with were unique in this regard.So anyone who's considering selling Haskell-based services to companies could very well be in a situation where any (L)GPL libraries are non-starters, regardless of actual legal concerns.