I seem to recall quite a bit of legitimate business was taking place on Silk Road which I guess makes some sense there was illegitimate profit ready to be spent. Unfortunately that didn't stop the legit money being stolen by the US government. And if it ain't law enforcement then it'll be the site operators themselves.
Yes, there were quite a few legal things being sold there:
Even if it's totally legal (since few goods are supposed to be restricted), the fact it sold on darknet marketplaces which allows illegal goods is enough for government to take everything.