[1]: https://en.wikipedia.org/wiki/Criticism_of_Mother_Teresa
But in this, I'm not so sure he was right. He let his penchant for being contrarian and dislike of religion get the better of him. Not the only time this happened.
Any more reason for this other than a psychological evaluation of Hitchens? He made an argument, you can speak to it. Is it a complicated objection that can't be summarized?
Hitchens not infrequently exaggerated some alleged crimes or misconduct from religious figures unfortunately. He usually had it by the right end of the stick in the general view IMHO, but could be sloppy on details. Classic case of "say something with enough confidence and people will believe you, especially if it confirms their preconceived notion" (in this case, religion=bad).
Is Signal perfect? No. But overall, it's not bad, and if we compare them to the average mobile phone app filled to the brim with dark patterns and tracking to the point where Apple felt the desire to build an entire feature to prevent this, they're almost mother Theresa.