Of course drug dealers don't want drugs legalized. DPR claimed he wasn't just a simple dealer but rather some ideological crusader for a better tomorrow (by which he meant: anarcho-capitalism, his idea of utopia). He wasn't only selling drugs remember, but also malware, forged documents, he experimented with selling weaponry, etc ...
Source?
LOL, this is public domain, everything Mike listed was sold on SR, and much more (stolen identities, stolen CC numbers, etc. etc.). Note that he said "experimented with selling weaponry", because SR sold firearms for a short while only. They stopped doing so because the sales volume was too small to justify maintaining "the armory" as they called it. The source for the former is the SR site, and for the latter DPR itself, who explained thoroughly why he stopped selling weapons in SR's forum... Which by the way was a very interesting read, I never was a user myself of SR, I'm not really interested in things that can get you to rot in jail, but I dug in SR's forums just out of curiosity because it was a fascinating underworld ecosystem.