The texts actually just say not speaking of the faults of renunciates (like seeing a monk drinking, you're not supposed to broadcast it to everyone as it harms the well-being of the sangha and community), though it doesn't say you can't challenge them on their opinions and criticize their statements. However, it isn't described like this at all. Criticism, both internal and external, is disdained and discouraged.
You have teachers tell people from the start to empty their cup and not have preconceived notions when listening to a teaching. This isn't a wise approach with critically thinking people who would much rather be able to debate and reason with a teacher rather than simply taking it all on faith or with a blank mind. Especially if you're addressing people who arn't entirely convinced about whatever it is you have to say.
This very point is what made me want to re-immerse myself in the Tibetan Tradition. I missed the conversations with my teachers where they challenged me to challenge them.
When I translate classes, Geshe la often begs for questions. When there aren't any he often says "better ask some questions otherwise I'll just read the text." When challenged and prodded, even to the point of argument, he and many of the well studied Geshes I have come to know are completely in their element. For them, the interaction during the Q&A segment is often their favourite part. Geshe la told me he learns new things from the students, and is motivated to continue his own investigation of the teachings due in part to these interactions.
This lively banter back and forth is something that I missed while in Taiwan and Thailand, though those traditions certainly have their strength. Maybe being such a big talker myself the Gelug tradition is a good fit for me! If I'm going to natter on about something it might be good if it is dharma.
(It is also maybe a weakness, like how I was interacting on the forum today for the equal amount of time I spent on preparing a text for the weekend. Have to be more disciplined tomorrow!)