I will argue _against_ MongoDB all day, but there is most certainly a time and place for it. If you have a real firehose of data, don't care too much about the accurateness, and really need good speed... MongoDB is not an awful choice.
Frankly I think it's still an awful choice given it's broken replication model.
Compare this to something like Elasticsearch, which is well-known (and well-documented) to have data loss in certain situations.