If you want eventually widespread adoption, the foundation of the currency cannot be illegal. This isn't even a case of questionable morality, there's some really obviously huge illegal transactions going through on Bitcoin.
If you're really so blind that you can't see why this is very bad news for widespread adoption of Bitcoin, you need to take a step back and see things more objectively.
You're making an inference based on conditional probabilities that is not supportable by logic and mathematics.
Bitcoin has widespread adoption among criminals because they cannot reasonably make use of personal checks or card-based payments. It is their best alternative to cash for certain use cases.
For everyone else, Bitcoin has to be better than a debit card, rather than better than cash. This requires widespread adoption and financial service businesses using Bitcoin.
The foundation of the currency has little to do with the character of early adopters. I don't judge my stereo by the pretentiousness of the first audiophile to review it. Likewise, I don't care that people use Bitcoin to buy weed. There are only two problems I have with Bitcoin:
1. I can't pay all my bills with it.
2. I can't get paid for my work with it.
I can certainly jump through additional hoops to convert my dollar-denominated bank accounts into Bitcoin, but that does not actually improve my life right now. I have no compelling reason to use Bitcoin other than a vague desire to have some long-term alternative to the existing financial service businesses.
I have no reason to believe that Bitcoin will be that long-term viable alternative. I think that such an alternative will likely emerge within the next decade, but I don't think I have seen it yet. I see potential. But I don't buy potential; I buy value.
The bad news for widespread adoption of Bitcoin is really that it hasn't happened yet.
If you're really so blind that you can't see why this is very bad news for widespread adoption of Bitcoin, you need to take a step back and see things more objectively.