Because, in contrary to you, I care if Bitcoin ever goes "large".
Actually I'd argue that widespread adoption by illegal industries could be the best thing that happens to Bitcoin at this time. The black market is HUGE, it has almost 1.5 trillion market value (according to Wikipedia). If only 0.1% of that jumped on the Bitcoin bandwagon it would drive the price and network hashrate through the roof, improving trust in the security of the network and enabling a lot of people and businesses to work for bitcoins full-time on legal industries, thus creating an adoption spiral. Considering the usual response time of government when it comes to regulating stuff on the internet, we would get a pretty good head start of uninterrupted explosive adoption, making it way harder for them to do something about it.
This a very good argument. I'm 97% satisfied and 75% convinced. (Contrary to
davout's pseudo-arguments which are mostly empty jibberish).
However, i'm still worried that adoption will be postponed by few years because of governments delegalizing bitcoin.
Anyway, I see that clearly I'm not convincing anybody here today, so i guess everybody have to learn truth the hard way.
Just don't say nobody warned you.