While I agree with the sentiment you're expressing here on some levels (people don't like it when you insult things they like, as they feel they need to defend their choice or themselves because of it), I don't think that quite applies here.

This is a case where, although the ultimate complaint of the author is the behavior of the product (which is documented, but un-intuitive in nature unless you've read up on the issue), it's the way in which he chose to frame the problem that is getting people upset.

This is a known issue, even if it seems like a completely poor design decision. The issue I think most people here are taking is that because the author did almost no research on the topic, he got himself into a problem, and is trying to blame it on Mongo.