Is the purpose of this infrastructure to facilitate all this criminality? Certainly not the sole purpose. Perhaps it was purposely build in a way that would allow scale and prevent censorship which enables many forms of criminality which a different architecture would have suppressed.
Typically the law is written quite differently. If there is a uncoincidental legal purpose, then infrastructure must be legal. Because many times the purpose of a specific technical measure can serve both a legal purpose and a criminal one. To ask merely of a technical measure serves a criminal purpose without regard to a greater purpose is to criminalize any censorship resistant network.
There's two vastly different talking points here, a) the Tor network and similar tech that could get caught in legalese crossfire and b) specific websites that utilize the above. I agree on your sentiment that a) should never be outlawed but the German text seems rather specifically worded to address b). Please be assured that I'm not trying arguing that these people have enough technical understanding to not make it unnecessarily broad and throw a) under the bus as well.
I believe my main point still stands, b) is the equivalent of me opening a corner shop advertised as "illegal arms deals" and pretty much legislated enough.