This thread includes numerous examples of people who did indeed have grave issues with Mongo. They're not any less valid that your own example (or the ones you link to). In these topics there's always going to be positive and negative takes, but calling people trolls because - again, like you -they voice their opinion is harsh.
Doesn't (b) have a certain burden of proof? Maybe he had a bug in his code? Maybe he did something weird with his server? Maybe he didn't follow upgrade directions properly? Maybe he got hacked? Is it really too much to ask for something verifiable? Steps to reproduce? Log files? Assuming that the person isn't just malicious, even a before and after of db.xx.count()?