... which should be taken as a sign of Signal's technical excellence.

Just consider: if you're looking for privacy-respecting, actually secure, reviewed, audited and tested to bone tech -- short of replicating the work yourself, who's assessment can you trust? Perhaps paradoxically, you should foremost trust the unspoken opinions of criminals. Because those people are likely betting their lives and freedoms on the tech choice. Barely any other group will approach such a choice with more vigor.

So, morals aside, that a technology is being used by criminals is actually a compliment to that technology.