Purely speculation but I strongly suspect the subset of malicious tor users engaging in child pornography and human trafficking is extremely, extremely small. The largest group of malicious users is most likely drug and cybercrime related. Is it worth decrying tor as a heaven for pedophiles or human traffickers if they make up a negligible number of users? If so, the same could easily be said about bitcoin or any other decentralised cryptocurrency. The benefits given to journalists, activists, or any individual who wants anonymity for the sake of pricacy is worth more, to me, than maybe helping a negligible number of users. Further, those malicious users would likely find another way to engage in their activities but could the legitimate users?

There are a bunch of similar projects where such people could (and likely already are) move: I2P, Freenet, GNUnet, and probably some others. So closing (or not supporting) Tor just because some bad actors are there is pointless. Every tool can be used for both good and bad things.