On the Yahoo groups discussion board for Philip Glass a fan dutifully expressed his feelings about trading bootlegs on the board.  As a practice off the board however, it was tacitly condoned.
I am not going to give a speech about intellectual property.  I was not always in the position that I'm in professionally.  I have made bootleg recordings myself and there are a great many commercially unavailable pieces by many composers that I'd love to hear and if the bootleg is the only way to get my hands on it, then so be it.  Again, I'm not here to preach.  I always tell myself that if there were to be a commercial recording, then I would buy it.
In regards to Philip Glass' music, in a bizarre way, the demand and success of Candyman on the bootleg market perhaps might have led to the eventual legitimate release of that music. 
Philip Glass for many years has worked very hard for things that would not have been possible had he not been so diligent and smart.  No one wanted to perform his music so he formed his own ensemble.  No one wanted to publish his music so he formed his own publishing company. He has started three record companies.  At the time of the release of The Hours in 2003, Nonesuch was producing one recording a year of Philip Glass's music.  In the past 3 years, Orange Mountain Music has produced close to 40 albums of Glass' music, many of which might not have been possible without a dedicated and ever growing audience who supports this music.
It's only years later, after a humble beginning, that an outward perception leads to believe that the composer "controls" his scores by not making some of them available for performance.  For many years (and still to this day) that "control" is his livlihood.  He writes music for piano, then takes to the road performing it.  It is his right to protect his work. 
This is not the same circumstance as a highly successful pop band with a large corporation behind it…this is a direct relationship between a composer and his public. Whether it's in regard to performances or recordings.
As for bootlegs in this light, with the existence of Orange Mountain Music, at this point to deal off the board in the trade of bootlegs, as a practical matter, diminishes the chances very greatly of a commerical recording ever coming to light.  I'd personally love to see commerical recordings of any of the 14 Philip Glass operas which have yet to be recorded.  I just understand better how bootlegs undermind that possibility more so today than ever before.