Three points: 1. The MPEG Layer 3 encoders and decoders used in Trisquel are free software (at least from a copyright perspective).
2. There may be patent issues in the United States potentially up to the year 2017* but not in other countries anymore. That's just because the US has absurd patent laws. As a non-American this is a non-issue to me, and probably the same for the majority of Trisquel users. 3. I do agree that we should promote free formats, but I don't think that removing MP3 support would be popular or constructive. * https://en.wikipedia.org/wiki/MP3#Licensing_and_patent_issues
