For what it's worth, the Catholic tradition has quite a long history of arguing that certain things which are immoral should not therefore also be illegal. 
I am drawn to the moral agnostic quality of the Bitcoin protocol, as you are. It presents a certain set of trade-offs that are very compelling in our present cultural and political setting, as well as in relationship to the weaknesses of human nature in general. But where I would draw the line versus where a true maximalist would draw it is at the point where this agnostic stance is used as the basis to order my own life and the life of society as a whole. I believe this is to commit the same error as those who subscribe to scientism. The scientific method is true and powerful, so far as it goes. The problem is when it is misused an exhaustive explanation of all of reality. 

The two cases you describe above are objectionable to many, agreed. How would you address a third case, namely: Those who are incapable of deciding for themselves whether or not pornography or marijuana are things they can enjoy without being enslaved or damaged by them? The difficulty is to recognize that some people, in the act of trying these things so as to determine whether or not they can enjoy them without abuse, will be compromised by the very act of trying them. 

 As a guy that falls somewhere on the spectrum between agnosticism and atheism—a “god of the gaps” guy, as a nod to your comment about the hazards of scientism—there’s one thing I know about Catholic priests in particular is that you folks are awfully well read. 

Anyway to respond to your question: I dunno really. In general I don’t think things should be illegal because some people misuse them. Not everyone will watch porn and become hopelessly addicted just like not everyone will buy guns and start murdering people. Let those people fail but also let there be strong safety nets to catch them and set them right… be they strong communities, institutions of faith, government programs, or whatever. 

Full discourse in case my bias is showing: I do enjoy me some occasional cannabis and pr0n