That's a 24-hour-news-network-pundit grade straw man he's created there. The replication strategy used by Cassandra is sourced from the Amazon Dynamo design (shared with Riak and Voldemort) and is intentional. It's not a bug; it's the way it's supposed to operate. There are many large scale distributed systems built on this replication strategy that have excellent durability track records -- Amazon S3 is one of them.

The back pressure argument is laughable. In Cassandra, a write consistency of greater than ONE will ensure the data is replicated to more than one node before acknowledging to the client.